ala115

Hello everyone. This is the first time I've ever been on here, and I'm not really sure which board I should be posting on, since I'm not sure what's wrong with me, so yeah.
Background I guess? I'm female, 19 (about to go into second year of college), 5'8", ~135 pounds, no known health issues, not the most active person but I'm not the laziest either (I use a bike on campus and stuff.)
The problem I guess started about halfway through my senior year (I was 17) when I had started feeling nauseous (I think the day before) and then 2 or 3 hours after dinner, I got diarrhea, and after that I vomited a couple of times. The nausea stuck around for the rest of the night (and the next morning but that might have been psychological- I really cannot stand vomit at all) but overall I was feeling better, either because it passed or because I had a Tums. About a month later almost the same thing happened. I hadn't been feeling nauseous that long beforehand, but for the most part the same thing happened. This same thing kept happening, but it got less severe each time until it was just gas (smelly gas I guess...) and then diarrhea, sometimes with nausea, sometimes without. And this was happening anywhere from 2 weeks apart to 2 months. In the meantime, I would frequently feel like something just wasn't quite right "down there" just because I felt like I just shouldn't be noticing my digestive system that much. (Really vague I know, but I guess you could say it seemed like my intestines were "gurgling" a lot.)
I went to the doctor after 6 or 7 months of this, and they drew blood, took urine and stool samples, all sorts of stuff, and nothing. The doctor said it might be IBS (the digestive problems catch-all -__-) or I just need to eat more fiber or something. -__-
Then, I went away to college, and I don't know what changed, but no digestive problems happened for the whole ~3 months I was there before christmas. All I could think of that'd I'd done different was try to avoid as much milk as I could. I knew a lot of people mis-diagnose themselves as lactose intolerant, but it seemed pretty likely in my case. The problems started up again over winter break, but they still weren't as bad for the next quarter, and I was still avoiding milk and cheese and stuff. Spring quarter I started taking Lactaid pills to see if those would help, and they seemed to, for the most part.
Now I'm back at home, and my "issues" have gone back to how they were before- much more frequent and worse than they have been when I was away. Then I started realizing: I don't think I'm lactose intolerant since I just had 2 slices of pizza with a pill for each slice (which is overkill I know) It's still just gas + diarrhea and sometimes nausea, but it just happened again, for the second time in one week! (Also the second time this week it has prevented me from hanging out with my friends, either from making me feel bad enough to stay home, or from me not wanting my bowels to revolt at someone else's house. -__- Sorry that's the thing that's really bugging me now- I'm almost used to whatever it is, but now it's messing up my social life and it's not like it's something I want to tell everyone about.)
As I said before, I tried avoiding milk/taking pills, but I've also tried cutting out soda (didn't work) and coffee (also hasn't worked.) Before, I didn't think it could be related to hormones and my period, but recently it seems to have happened during "my time of the month" so that might be it? It seems like I'm having some sort of reaction to a food because of how often it happens, but this has happened after anything from In 'n Out burger to sushi. And it's not something like bread (with the gluten thing) because I have bread like every day.

Sorry if that seemed like I was rambling on, but it feels like it's been happening for forever and I'm just tired of not knowing what's going on. If anyone has any ideas of food to try avoiding or other things that might be going on or similar stories, sharing would be nice.