C.H.
Happened to me too. I'm not taking any birth control so for me it has nothing to do with that at all. I spoke to my gyne and he said it's the number one complaint he gets from moms.
He said it's due to having kids and me taking on the bulk of the responsibility and chances are I'm frustrated with my husband and that my emotional needs aren't being met due to all the stress and frustration. He also stressed the importance of speaking up and letting my husband know I need more help from him and that we should make time for each other (go on dates - ha!... haven't done that in years).