Sex drive

My husband is a nympho. We have 3 kids, the two girls are his from a past relationship and the boy is mine from a past relationship.  We got together when I was 6 months pregnant. During the end of my pregnancy and for about 3 months after I had my son (feb 6, 2011) I was also a nympho but after that I am never in the mood anymore and it's hard for me to get into the mood. Lately I have been having sex with my husband just so he doesn't get upset. We have sex maybe 2 times a week. What can I do to get my sex drive back up? I'm scared that if I don't he will find someone else. Please help!!!!!!!!!