Could this be early labor signs?

A little TMI.

Last night around 10 my so and I had sex not even 20 minutes later I had horrible period like cramps on and off for about 2 hours or so. I was able to get to sleep so i didn't think nothing about it. Today I maybe had like 3 or 4 of cramps but nothing to bad but I have had mid to lower back pain all day today. I have tried Tylenol, heating pad, warm bath, and even drinking more water and nothing has helped. I am only 36 weeks and this is my first. I just don't know if these are signs of labor or if I am just over thinking it.