Yes, Tylenol is safe, but contact your doctor if you are worried or if you want to take anything else.
As pp said, this is just the beginning. You'll have cramps, then stretching ligaments, then Braxton Hicks contractions, then real contractions, and then cramps again after the baby is born and your uterus shrinks again. It's the miracle of life.
Staying well hydrated can sometimes help, but mostly you've just got to go with it.