I've had regular bowel movements and i'm 21weeks pregnant and there's a lot of pressure on my tailbone and i feel like i have to push. is it normal?

No: It can be normal to have a pressure sensation in the pelvis during pregnancy, but I would want you to share this with your doctor. She/he may consider doing a cervical length to make sure there's been no cervical shortening and to make sure placenta in normal position. More information/reassurance is needed so you can know this is 'normal' amount of pressure