Preterm labor?

I turned 26 weeks yesterday. On Saturday I was having lower back pain all day (I vacuumed the night before and that usually kills my back so I assumed that was the reason) and later in the day I started getting a lot of pressure in my butt and cervix. The pressure eventually subsided but the back pain never went away. Yesterday I still had some lower back pain but not as bad. Around 7pm I started getting period like cramping that was constant, like it wasn't coming and going it was just there for like 30 minutes on my lower belly/back. Then it started coming in waves but irregular. Some were 2-3 minutes apart, some were 10-15. Some longer some shorter. I was laying down and drinking water and it took about 2.5-3 hours to go away but it did and I haven't had any cramping since. No blood, no crazy discharge. Does this sound like preterm labor, irritable uterus? Should I still call my doctor even though it stopped over 12 hours ago? I have a small subchorionic hematoma and a suspected low lying placenta that I'm getting another in depth scan for in 2 weeks.