Wayyyyyy too long contractions...

So I'm wondering if anyone has had any of this and maybe got an answer?

All day I've had contractions that feel like they last 10 or 15 minutes each. My belly has been almost constantly rock hard, baby all balled up. My back aches and I'm really uncomfortable but the pain is manageable. I also have been shrinking at each of my last 3 appointments, going from 34 cm at 33 wks to 30 cm at 34, then 27 cm at 35 wks. My baby is so tight in there it seems like she's shrink wrapped. I've also lost about 10 lbs in the last month. And I started underweight. I'm 5ft10 and 136lbs right now at 36 wks. But my baby has measured big at every scan. The last one was at 33 wks. I'm having an ultrasound tomorrow because of my shrinking, to check baby's growth and my fluid levels. Has anyone else had any of those issues?