hello all!

I'm not really a veggie grower, more of a tropical guy so I'm not well educated on veggie gardening. Tried looking around but couldn't find any answers. I decided to try seeds of super sweet 100's that I found at the grocery store. Started them indoors around March 15th, and put them outside maybe a month or two later. In the beginning they started out tasting wonderfully, full and a nice balance of sweet and acidic but over the last few weeks the fruit has begun to taste pretty sour, and the fruits are a bit smaller. Can you tell me what I'm doing wrong?

Heres a little bit about how I grow it:

Its in a container, admittedly (and I know this is wrong) there are 4 tomato plants in this container. Watered everyday for the most part. I fertilize with bloom booster (3-12-6) or kelp extract when I think about it, usually once every three weeks or so. They get direct light from about 11am-Sunset.

Thank you for your help!