I remember like it was yesterday when i lost my mucous plug with my son, it wasn't just globby, it had veiny things in it...it is too early for you to be losing it. Probably just discharge which i have read is normal...
Cramps are normal especially at 21 weeks. I'll be 22 tomorrow and it's basically strecthing of your uterus and round ligament pains, it's normal BUT if it gets too unbearable or followed with bleeding call your doctor. As far as the mucus plug it's too soon to lose it and it's probably discharge. I've been having thick discharge lately just keep monitoring it.
cramps are normal as everything is continuing to move and stretch...ive never lost my mucous plug to my knowledge, but i have thick white/clear discharge all the time. so it could be either. with that said if it is your mucous plug it can regrow, i wouldn't worry about it. just keep an eye on it...if you lose the whole thing you should call the doc so they can make sure you're not about to go into premature labor.