Am I going into premature labor or am I just being paranoid?

Well my boyfriend and I just found out that we are expecting. I believe that I'm somewhere between 18 and 22 weeks along. We haven't made it to a doctor to confirm that though. Anyways in the past 18 hours or so I have been having terrible cramps and backaches. Also, it feels as if my belly has "dropped" and hardened a significant noticable amount. I also have felt no movement from the baby in about 8 hours. I don't know if I'm in the process of a miscarriage or if I'm going into premature labor, but I need advice. Thanks so much. I apologise for any typos...