Sabrina - I just wanted to give you a more thorough explanation of what I was explaining in my last message. Hopefully, my suggestions will work well for you going forward.
So, as I mentioned, when you point your camera at an object and set your exposure in camera to "properly" expose, the camera is always trying to make whatever you are pointing it at 18% gray.
If you have a white background and want the background to be white, you will need to overexpose the background to get it to the right level.
If you are using a black background, you will need to underexpose the image to avoid making the black look too light.
It's important to get your settings set up prior to adding your products into the picture. They will add more colors for the camera to decide to over or under expose. Black and White colors are easy to use because they are pretty standard shades and you can pretty consistently guess how much to over or underexpose to get a correct exposure. If you were using an 18% gray card, you COULD meter off of that and set your exposure right in the middle and get a perfect exposure. These can be purchased cheaply online or at most camera stores for $10 or less. Just make sure you have the same light on the card that you will have on your subjects.
You CAN still use a light modifier and I'd highly recommend it. I think with the products you are offering, it will give your products a more professional/clean look. The use of a white box and a diffuser will help you only have nice white reflections on your products instead of possible reflections from things within your home. From what I saw on your website, you are already doing an excellent job with all of that. You're just having some issues with the camera trying to make everything gray.
I wanted to show you some test shots I did with a very simple set up. Obviously, with your setup, I think you will get MUCH better results.
All I used was a torn piece of seamless white background paper, a $30 video light and a tripod (plus my camera).
I only metered with the camera's built in meter and used Auto white balance to get the white balance I liked.
When I started, the images looked too dark. All I did was adjust my shutter speed (slowed it down) until it over exposed it by about 1 stop.
After trying that, I felt like it was still a little too dark, but I didn't want to slow my shutter speed down much more (I was using a 100 mm lens and was already shooting at 1/80 of a second). General rule of thumb is you should shoot at 1/100 with that setup. You usually want to shoot at 1/whatever focal length your lens is. A 50mm lens can be handheld at 1/50, etc. So, I was already slower than I'd like to be.
I fixed it by increasing my ISO. By doing that, the camera was more sensitive to light and it caused the camera to overexpose even more.
At that point, I felt pretty good, but I wanted to fine tune it a bit and I started playing with my f stop. When you adjust your fstop to a smaller number, it will let more light in which will overexpose your image even more. If you want it to be a bit darker, you need to make the f stop bigger. Instead of a f stop of 3.5, you may want to increase it to a 4.0 or a 5.6, etc. It will let in less light and you can fine tune it even more.
Basically, there are a lot of ways to get to your desired result which is to overexpose your white background by 1-2 stops. Or underexpose for a black background.
Below are the results of what I managed in about 7 minutes of messing around. You will get MUCH better results with your setup. The nice thing is once you find a setting that you like, as long as you don't change your lighting and such, you can keep those settings for all of the objects you are photographing.
Make sure that if you are going to use a light modifier, that you have that modifier on and being used when you meter your box. You want to meter it with the light that will be on your product.
Hope all that makes sense! Here are the results of my test shots.
Better, but still a bit dark and yellow - I believe it was set to a flash white balance setting from a previous use. I changed it to Auto white balance after this.
I continued to fine tune until I liked how my background looked and I changed the white balance to auto since I had mixed lighting on my subject. (LED light and a tungsten lamp). Auto white balance gives it a nice balance. If you know exactly the type of lighting you are using, you can put that in for your white balance or again, there are more things you can purchase to set your white balance and get it perfect, but for simplicity and financial sake, this is an easy work around.
At this point, I felt pretty good about it. Now that I'm looking at it again, I probably could have went a little brighter. The background is still a touch gray, but that's just a simple fix of either slowing down my shutter speed, increasing my ISO, OR opening up my f stop by making the number smaller and allowing more light in. And again, once you find the sweet spot, you're GOLDEN!
Hope this all helps! I wanted to do it in the most ghetto, simple way so you could feel even more confident with your nicer setup. You can do it! Your blog looks great and honestly, your pictures aren't bad! You're just going to make them a little better! :) Keep up the great work!!
P.S. Feel free to let me know if you have any questions I can answer or help with. I love talking photography with people.