I understand completely how you feel: I have a similar situation. I'm 19 weeks on my first but my partner has two sons (13 & 11). I have found he has not been excited, interested or even positive about this pregnancy. He is going through a tough time with a custody and finance battle with his ex-wife, so we have decided not to tell his kids until that is over (hopefully July/August), so I also need to keep my pregnancy hidden. I have only told a select few friends who I know will be discreet. He has told none of his family or friends yet. I have found it very depressing and difficult that his excitement is not what it should be and it really brings me down. He even missed 2 hospital appointments and I cried almost uncontrollably because of this. I brought all of this to his attention and it took a few weeks to get through, including me telling him I didn't wasn't to see him again, so he had to stay with his brother for 3 days. All is much better now, though not perfect yet. I made it clear that I need him to be positive, interested and make an effort; that his lack of interest and excitement (which he said was my perception but not the case) was making me depressed. I genuinely think that he would be more interested/involved if we didn't have so much other crap going on in our lives. So I try hold on to that when I find it hard. Definitely telling him how his behaviour makes me feel and what I need him to do has improved things: it was very hard for me to approach in the first place, as I was feeling fragile and wanted/needed him to make an effort unprompted. I think it does sound as if your husband is genuinely tired. I think you need to tell him all of what you feel and let him know how to put it right for you. Pregnancy is tough and you need a lot of support, perhaps he has forgotten this because you've been through it all before a few times. If he's like my man, you'll have to tell him a few times to get through and tell him in detail: I need you there, supportive, interested and awake!!! Best of luck. I'm sure you will get through it. After all you've got through child rearing, which is one of the toughest strains on a relationship!
I also work graveyard shift n had to go to the hospital with my husband when he was having minor surgery. I was just simply exhausted from work since I went straight from working midnight to the hospital with him. I swear I was so concerned but I was so tired that I fell asleep and when the doctor came in and explain the procedure. I missed it all. I was asleep in the room sitting on a chair. He later told me that the doctor looked at me n my husband said oh she is really worried.. As a joke lol I tried to stay awake n be involved but midnight shift takes a toll on ur body that at certain point you can't function. I think your husband is just exhausted n need a break.
It can be very wearing to be at the doctor's and just wait and wait and wait, especially when you are not the patient. My poor husband has waited around when I was doing IVF transfers so many times, it's really pretty excruciating for anyone who is not the primary party. And that's not the husband, sorry to say.
Your husband frankly just sounds exhausted. See what he says to you some weekend morning after he has had a full ten hours' sleep. He might be a lot more upbeat than you think.