Feeling lonely in marriage

Hi ladies, my husband and I have a 3 year old little boy who has Cystic Fibrosis. I'm a stay at home mom and feeling very lonely. My husband works full time as an assistant manager at a deli. I understand that working full time outside of the home is draining, but it's like pulling teeth trying to get my husband to do things with us. For example, I will ask him to go for a walk with us and he sighs and says, "sure.." or he just won't go at all. On his days off, he will stay up until 3 in the morning and sleep until 3 in the afternoon if I don't wake him up. When he finally gets up, he isn't as involved as he should be. This isn't new. Prior to getting pregnant, we would stay up together and sleep all day, but that quickly got old to me because I enjoy being active. I expected a change once our son was born. We have talked about these issues and he acknowledges that there may be a medical reason for his sleep habits. However, he hasn't seen a doctor and lacks the motivation to do so. I struggle with depression, anxiety, and I feel like a single parent quite often I am so lonely. We had a conversation last week, where my husband broke down and apologized for not being involved. We covered a lot of ground and things started to feel better. a few days go by, and I am struggling with these same feelings again. am I expecting too much? I see families together when I take my son out and it hurts. I realize that this is all over the place, but I'm trying to give as much background as possible and let it be known that I'm not coming from a place of blame shifting. Am I justified in feeling the way that I do?