Peanut butter and celery is one of the few things I can eat without gagging. I told my OB and he said it was a good source of protein. Double check with your doc, mine said no problem.
I actually read that one of the ways to keep a kid from having peanut allergies (if you don't have them) is to eat peanuts during pregnancy. Please check me on that, though. Just google "eating peanuts in pregnancy."
I eat peanut butter on the weekends all the time. If you have peanut or nut allergies in your family it may be best to stay away from it until your kiddo is old enough to be tested for allergies. Ask your doc if you are unsure :)