I am 18 weeks pregnant. Is it normal to experience vaginal discomfort inside? (Burning, itching, pain, etc.) During sex, it becomes increasingly painful and burns a lot. IS THIS NORMAL?

It sounds like you have a yeast infection which is very common during pregnancy. You will need to tell your midwife or your doctor as soon as possible so they can advice you on what to take.
Good luck and congratulations on the pregnancy.

During my first trimester I experienced pain during sex but it was because everything was tight and more sensitive. I would call your doctor and get checked out. Good luck!

It could be several things. It could be an infection(bladder or vaginal etc), it could be extra sensitivity due to increased blood flow/swelling that occurs during pregnancy, etc. Do you have foul smelling, oddly textured or discolored discharge? Is it all the time, or only during sex that you have the pain? Its not uncommon at all to get infections when pregnant. It is important that you immediately contact your physician and tell them about this problem. Most likely they will have you come in and do a few tests and help you get things taken care of quickly. It may be nothing, but if it is an infection, and you leave it for too long it can become serious and potentially dangerous to mother and baby, so make sure you get things checked out soon. (for example, a bladder infection left alone for too long can cause serious kidney problems.)