Cindy, it takes time to build up strength in muscles that you are not using so give it time. You could try supporting your neck with your hand but it is important that you do not pull on your neck in order not to give yourself a strain.
I have been lazy wrt to tummy exercise (I use to do about 200 crunches, cycles, leg lifts!). I will do 50 crunches this evening to kick start my exercise regime.