Help. Scared of preterm labor.

Samantha
I'm 28 weeks... I started having these sharp cramps today that only lasted a couple seconds but went on all day. The last couple days I have felt nauseous and have been having loose stools... I don't know if I ate something bad or if I have a stomach bug or just something from pregnancy. I contacted the OB nurse and she said if they become consistent to start to count them. Well I'm sure there were a couple times where I had the pain more than 6 times in an hour but they had no rhythm and I don't feel tightening. I'm currently resting and I feel baby moving around. Right now, I have like a very mild Achy cramping and slight back pain... I have also been very gassy... I would like to know your experiences... I'm a FTM and I am not sure if this is just my third trimester symptoms or if this is something I really need to watch out for.