Why would I randomly start vomiting up sugary cakes or sweets?

Randomly a few months ago I had eaten something called a Zebra Cake which is just a little cake with cream in the middle. Later that night I vomited it up. Then maybe a month later, I ate something else I really cant remember but it was sugary, i think it was some sorta cake or something. Again that night I vomited it up. Then maybe a month ago I had some donuts from a home made donuts place down the street from my house. And i had had them with breakfast, that night again i threw it up. Though i noticed, If I eat chocolate it doesn't bother me, cookies it doesn't really bother me. Oreos a little bit. I have been testing what I can eat. But last night, I had some watermelon[i love fruit] and I had that feeling in my stomach like I had to vomit but thankfully I didn't. Why the hell would this be? I use to always eat stuff like this[not all the time maybe once or twice a month or something.] I don't really eat cakes or donuts anymore. Sometimes chocolate, sometimes cookies.. but not as often as I use to. I don't understand why would this be happening. Yes I have STOPPED eating that crap I just want to know why it was happening. [I am not over weight, I am actually very small I'm under weight and I have trouble gaining weight, I am 4'11 and 80 pounds.]