Girls, hello! I'm at week 34 and I wonder what it could be? Today nigh…

Girls, hello! I'm at week 34 and I wonder what it could be? Today night I woke up from something that really hurt my belly, like with severe constipation (sorry but I can't say anything else ?). It was such a heavy feeling, and my belly felt like a stone... I have an appointment only tomorrow... I'm very worried now. My belly is also slightly hard now, but there's no pain.