Confused

I have missed my period. Not a trace or symptom of it except light cramping. My husband and I dont use birth control but for five years our method of avoiding pregnancy has worked. He says he didnt (ya know) and he is sure we are not expecting. Any other suggestions? I am not under any stress, have been exercising, but no more than usual, and no extreme weight loss or gain. I Googled and thats the other alternatives that were given.