Should I be concerned?

I'm 33 weeks pregnant based off my last period(I'm pretty positive I'm at least 35.) The midwives keep commenting how big the baby is when they measure him at my appointments. Everyone keeps saying how big my belly is already too. (his head is also in position) I've been having braxton hicks contractions occasionally during the day when bending over, etc. The night before last I had three extremely painful contractions within a 15 min period while lying down in bed that almost made me want to go to the doctor just to check but they seemed to stop. My midwife said not to worry about the contractions if they stopped. Now all yesterday and today, I threw up once and I've been having bad stomach pains and diarrhea. I just want to make sure I'm not going into premature labor or if I should be concerned. This is my first baby, I'm due Aug 10th and the midwives aren't being very helpful when I ask them things because I haven't reached 35 wks yet