Honestly, it sounds like what I had. Around 28 weeks I started having some pubis symphysis or whatever it's called. I couldn't stand. I couldn't walk. I couldn't lift my legs high enough to put on pants. I couldn't even shift positions in bed because it was straight up AGONY. My doctors blew it off and told me to get a belly band. Did not help at all. It lasted a few weeks but it DID get better. It's not dangerous but it's really uncomfortable. It feels like your hip and pelvic bones because it is. I could even feel them scraping against each other, I swear. Like I said, it's excruciating, but not dangerous.
This is my second pregnancy im 15 weeks and im starting to get that way. Most likely is round ligament pain. They told me mine would most likely be worse this pregnancy die to scar tissue from the previous c section
Sorry to hear you're in pain.. unfortunately I doubt it's preterm labor, it's just pregnancy.. and with each pregnancy it gets worse. This is my third and I'm having your exact symptoms and I'm only 23 weeks. This is the most painful out of all the pregnancies and I also thought I was in labor but it really is just the pains of pregnancy.. try to sleep with a pillow between your legs for the hip pain.
My hips killed me up until I started my third trimester, when it finally subsided! They said it was my body making room for baby. Sleeping on the sides definitely made it worse! Good luck and God bless!