How do I eat healthy with only a $100/month budget?

I got hospitalized last year and I am in debt because of it. Also because of my illness I've ran up some credit card debt. And because of just plain stupidity, I signed an apartment and car lease that was too expensive for me.

Basically, while I slowly dig my way out, I don't really have much to spare. I only have a $100 to spare for groceries every month. Initially I was just going to go back to eating white rice and hot sauce, but then I remembered my friend telling me about this sub and how good you guys are at making shit work for you.

Should add, I'm really allergic to shellfish. Like, even being in the vicinity of it makes me start itching and having minor trouble breathing.

So, help me /r/frugal, you're my only hope.

Edit: Should I go to places like the dollar tree, or does it not a make difference? I have a Harris Teeter right in front of my apartment. That's where I usually go.