To be worried he doesn't want sex

Exactly, especially not three months in. Major red flag!

I disagree with the porn thing above.

It was good for months, so he's willing and capable. I honestly think it's a 'too much of a good thing' thing.

I love sex and don't get enough of it, but I've been in relationships where it started off daily. I honestly got a bit tired of it after a few months because it got a bit routine.

Let the drought happen a bit. He'll be back.

Yes
If he’s finding his job exhausting now, how will he feel in say 10 years time.Does he smoke?
(l’m not referring to cigarettes) This can lower sex drive.

I agree with this. It may not be but porn addiction affects men’s intimacy. You are young and I just wouldn’t waste my time trying to figure out his problem that early on in a relationship.

You say he wants it when you’re half asleep. Could be that there are no demands or judgement on him. Could be anxiety.

The right persona to be partaking in lots and lots of porn and having erectile dysfunction.

Run, don’t walk.

Get out of there. He could have a physical issue, he could be watching a lot of porn (most likely), or he could be playing games (sexual withholding) as this is a very effective weapon.

If you really like him ask him to seek help, but I wouldn’t bother. Just leave, these men only get worse until you’re a shell of yourself.

Does he drink after work? This can affect sex drive. He should have his testestrone checked anyhow. If it is work related at this stage of a relationship on his day off he would probably want it then. The fact that you do most of the work is a bad sign. I had a partner like that once and it got worse over time. You both are very young for this to be happening. If he works a physical job under 50 hours a week he should still want it on his day off. If he is doing physical labor 70 hours a week I can see where physically he has nothing left. I personally had a physical job working 50 hour a week and we still did it on my day off once a week after some rest, I got up every day at 4 am so the rest of the week was a blur of exhaustion. If he works construction they can be seasonal and during the busy months it’s work till you die mentality. During the slow months you might notice a change. He can get a hormone check or go to a therapist, other than that you can wait and see what happens over time. This may just be his preference for his sex life. At that age it would be a deal breaker for me. I lived like that for 7 years because I was in love and he was my best friend. Don’t waste your youth if he doesn’t get help or figure out the why. My daughters partner doesn’t initiate it as much as she does but sometimes he still does so that’s enough, his brain needs more encouragement. For example she will get new bras and his brain gets activated. But for sure she usually initiates sex most of the time.

At 29 he's in prime physical fitness. If he's struggling to do his job now what's he going to be like at 49.

I appreciate this thread isn't for this question but he might want to think about his options and get trained up in something else or go for promotion to a less physical role.

Nobody deserves to be knackered all the time.

It's a really good sign that he's opened up to you on his own initiative. I think a lot of men would bottle it up or feel too embarrassed to talk about it.

If he's tired from his job that seems to be the most likely reason; does he have a break or a holiday coming up to get his energy back?

If he's stressed or anxious for any other reason that could also be an explanation. Beyond tiredness and stress there could be medical reasons that a GP could help with.

While I understand it makes you feel unwanted, I don't think it would do either of you any good to focus on that, because it's almost certainly not because of you.

After three months, I wouldn't say it was normal. But I get the work situation as my partner is also in a physical job. My partner also has chronic pain issues and low testosterone count so sex life has been challenging in the last 6 months but, certainly, for the first 3 months in a relationship it was not an issue and we managed about once a week (bearing in mind we didn't lived on opposite ends of the city and didn't see each other daily).
Sounds like he is aware and open about it so I don't think there is a fundamental problem with the relationship. Something else might be going on which is affecting his sex drive. Find other pressure-free ways to connect for now and see how it goes.