Terrible menstral like cramp during pregnancy.?

im currently having a constant menstral like cramp in my low abdominal. Its not like a cramp and it goes away then comes back, its just a persistant cramp that eases up momentarilly but is still there that is moderatly painful and i have a high pain tolerence. i also have slight back pain. I feel like vomiting as well. im 36 weeks pregnant in my 37 week. i cant time it because its persistant. what should i do? what could this be?