Help! Anyone else had this happen?

I'll try to keep it short, but I am 18 weeks pregnant and on Monday my husband and I had sex. I've been feeling a weird pressure when we do so we try to find the best position and just ride it out (no pun intended). After we were done I had some cramping/lingering pressure for about 20-30 minutes before it subsided. Then yesterday I noticed I had some light cramping, which is actually normal for me up to this point, but in a slightly odd spot. Last night I suddenly had a lot of discharge that looked like a mucus plug but it was all white with a tiny spot of brown in there; so faint that I barely caught it. I sent a message to my doctor just to confirm that it was normal and left it alone for the night.