really bad pain in tummy any ideas?

Hey ladies so I can't get in to see my midwife till 7th march, but today I've got a nasty sharp pain / pulled muscle pain to the right of my belly button I'm 31 weeks pregnant baby's moving round fine but it really hurts n won't seem to go away n my belly seems to feel like hard n tight if I'm sat forward n then lean back the pain intensifies does anyone know what it may be?