I have a problem with my boyfriend and my son...?

I had our son on 11th September and since then his dad's seen him 3 times. He says he's "busy", but how can he be too busy to see his own son? He was supposed to be moving in with us but he decided he's better off at his mum's (we're only 16)... He's looking after our son now because I'm ill and I don't want to get my baby ill too. But he hardly ever spends time with him? I don't want them to get estranged but I don't know what to do? :(