What causes the pressure and pain around 30 weeks in the low abdomen?

When I walk it feels wierd down there it feels like a lot of pressure and it hurts and if I walk too much it actually burns…A few days ago it was the worst it was burning and so painful…There is pressure on my bladder and maybe other things…I think the baby moved positions possibly cause also today I'm noticing movement higher then it has ever been…Is it too early for the head to engage? Can it just go upside down without engaging? Do I need to worry about anything? How do you deal with the pain?