confused, is this normal?

So when my husband and I first started dating, we literally were in the "jack rabbit" stage. Now we have been together for 4 years and married a few months and we have sex on a normal basis, but my husband gets off extremely fast and he always says sorry and feels bad but it's every time and he says he can't continue because he already finished and he lost stamina and then I proceed to finish my self. Well I enjoy sex with my husband but I honestly don't understand why he finishes so quick.. I spoke to my bestfriend and she said that is normal and he should be back to his  regular sex monster self before long, and were we are newlyweds the sex may be more intensified for him. Opinions?