Pressure in my nether regions...anyone else?

Every now and then, I get a lot of downward pressure behind my pelvis, like I have a 10 pound water balloon up my lady part. After sex on Sunday, it was more pressure than it had been before and really uncomfortable for about an hour. There's no cramping or spotting or anything else. At my seven week appointment my OB said I have a sensitive cervix.  I sometimes feel the pressure I'm talking about when I get up after laying down sleeping. I'm going to talk to my doctor at our next appt. Just looking for anyone's thoughts, especially if you have or have had this.