Why won't he touch me?

My babies dad and I met literally 2 weeks before we found out we were pregnant. She will be four in September and for the first few months of our pregnancy our sex life was still amazing. After the baby things dwindled and now it's like we are just people who share a bed. We have sex once every 4 months maybe. We've tried talking about it but it never changes. I'm getting frustrated by the fact that I'm lonely and I don't feel wanted. I've asked him if he wants to leave or find someone else and he always says no he loves me so much. I just needed to vent, thank you for any replies!