Rarely have ever been nauseous now it seems I always am

I'm 19 years old and until just 3 months ago I used to jokingly brag how I hadn't threw up at all since I was in kindergarten. And from what I can recall I was very rarely nauseous . The last time I was probably ever nauseous was I'm sure a really really long time ago.. I had absolutely no problems with being carsick, in fact I didn't even really get what that meant... I was able to eat a ton without being sick after, I was known for having a huge appetite.. and I could exercise intensely without getting sick at all.... until recently.

In May, after a week of feeling nauseous after eating, I went to the doctor and they told me I may have had a stomach infection(something I ate)and they released me from emergency but told me to go to my doctor. So 4 days later after feeling slightly nauseous but better, I went to my doctor and supposedly my white blood cells were back to normal so she said I should be fine, it must of just been a bug, but to come back if my nauseousness persisted.
Fortunately for about a month I felt great and then one day I ran a 5k and felt nauseous the whole run because I stupidly drank gatorade too soon before (at the time I was positive gatorade was the culprit) I ran through it the entire race( i was nauseous from the beginning) and at the end I went to gag like 3x but nothing came out and I was nauseous for the rest of the day. The next day came and I was pretty sure I wouldn't be nauseous anymore because I was pretty sure that the only reason I was nauseous was because I drank gatorade too soon before a run. But unfortunately from that very day, it like incited my nausea again, and ever since I've been getting nauseous so much. I have not thrown up since May but I get nauseous for almost everything now and its so irritating. Now I get nauseous in every long trip, after most meals, almost everytime I run now or exercise. Usually I would get lil butterflies in my stomach before doing something even slightly nerve wrecking, now I just get super nauseous . Another thing that stirs nauseousness in me actually is drinking water, in the case of today. Needless to say, my appetite is sooo much smaller now. (I do eat though) I don't know what this could be. Its definitely been something stressing me out lately.

I would appreciate help so much on this subject,
Thank you very much in advance.
Sorry for explaining so much, I just feel it is all so weird how from one second to another I was never sick and now I'm always.