M.
I hate to tell you, but you have sooo much time to decide this. Take every precaution you can to not get pregnant at this time. Two kids are really expensive - and they only cost more the older they get. Your kids deserve the best, so finish college and get a great job first. Make sure your fiancee does the same. Then get married - then decide on the next baby. The one you have now will love being the center of your attention for a little longer. Good luck!