Need Advice, Long Post- Please Read!!

I'm not sure if this is the right room to post it- but it does regard health issues. Hoping to reach a wider audience in hope of some sort of answers since I'm sleep deprived and crying while typing this.

My 2 year old (just turned 2 in beginning of Apr) is having stomach issues. Around her bday (5th) we traveled to Jax FL for a small birthday trip for her and big sister. We stayed about 3-4 days and on the last evening before we came home she started to have diarrhea. I assumed it was traveler's diarrhea (we are located 3 hours away in another state), and just made sure to hydrate properly. The next evening by the time we get home, the diarrhea has gotten so bad to where it's coming every 15-30 minutes and her butt is in pain (not from rash but her butthole from pooping so much). I broke down and gave her some children's anti-diarrheal medicine still assuming it was just from traveling since we dont do that very often. Well after the half dose I gave her, it went away from about 2 1/2 days. Then it came back by that Friday. By Saturday it was awful and i finally thought that well maybe it was something more serious. I took her to the walk in clinic and they assumed rotavirus, and had me take a sample of diarrhea to the local hospital lab. They said there wasn't anything you could so except hydrate and let it run its course. Well 2 days later, it clears up and I'm relieved. Never heard back from lab on sample. About almost 2 weeks later (earlier this week), the damn diarrhea came back. Luckily, it was Tuesday and her pediatrician was open to call and discuss it. She said the lab reports were all clear everything was negative. She said since the labs were clear, to start her on probiotics to see if that would help. She wasn't having any other issues during the duration of this and was happy and normal other than the diarrhea. So Tuesday evening, I started her on the chewable probiotic tablets (because local places were out of cultural packets), and it helped SO much with the diarrhea! It took about 2-3 days to start working. Well here we are Saturday/Sunday am, and she now has a burning fever and just vomited the tylenol and juice/water mix I gave her (luckily it was after about 10-15 minutes so I think it got absorbed). She kept gagging before she threw up. The fever has came down but I'm just at a loss on what the hell to do. She's luckily back asleep but I'm upset can't sleep because I'm scared she's going to vomit in her sleep and choke. She has been irritable somewhat and hasn't ate quite normal today but I've made sure she's had liquids. Can probiotics sometimes have negative effects even tho they helped just a day or 2 ago?! I feel like a mom failure and just want my baby back to normal. Has anybody else had a similar situation? Please, any advice at all at this point I'm desperate for answers! At this point I feel like it is something more serious (that is what my gut is telling me) despite what labs are saying.

Also wanted to mention that nobody else in household is having issues what so ever so don't think its contagious...? (8 yo old sister, me, nor husband)