I'm also 28 weeks, I'm in the same boat as you. Your stomach is gonna keep getting g tighter the bigger the baby gets, and the closer you get to your due date, the pressure will increase on your vagina. Laying down helps. When is your due date?
Mine started to really get more frequent and strong at 32 weeks. It's almost all day long but yes it's your whole stomach tightening . Not your vagina.
I keep getting those feelings too for about a week now the pressure isn't all the time but happens often. My discharge has also increased but I'm 18+2 so I'm going is normal!
You don't feel Braxton hicks in your vagina you feel it in your uterus. I had a lot of pressure on my cervix though during my pregnancy because my baby was so low, so maybe that's what you're experiencing