Knee Ache During Pregnancy

I’m 20 weeks pregnant and I’ve been having some serious pain in my knees when I sit on the toilet (anything below 90 degrees for example) or floor. It’s making it hard to use the washroom because I literally have to hold onto something to sit down or I sort of drop onto the seat which I don’t think is safe. I’ve had a similar pain before but after a bit of a weightloss it went away and now that I’m back at that weight I think that’s why it’s come back.

Should I be doing any exercises? Has anyone had this during their pregnancy?