Am I being selfish?????

Nicole • Mother of three beautiful children and a happy wife of 10 years. I have one simple mantra that i follow; live, laugh, love. If you have happiness, love and family, everything else is a perk :-)
So my husband an I have been TTC for about a year now with no luck. I am 29 he is 35 so we are at our prime. We have 3 beautiful children already and I want to add one more to complete our family. I almost feel as though it's god's way of saying that's it but I just cannot get the yearning for another child to pass. Am I just being selfish?