Please help with newly adopted greyhound and restlessness

Hi all, I am in desperate need of some advice and you guys seem to always know what’s best.

I’ve had my rescue greyhound since December and most of the time he’s an angel. It was mostly easy settling him in with his routine and we went for a while with almost no issues - he is(was) walked at 6am for 20 mins, then another 20 mins at lunchtime, then 45-1hour long walks at about 17:30 with meals at 6:30 and 18:30 and he seemed happy. He would be left on his own for 4ish hours in the morning and afternoon and slept mostly, then slept in the evening. He seemed really happy.

Recently though he seems to have regressed and I’m worried he’s bored and we can’t give him what he needs. He has begun waking us at 3:45am EVERY. MORNING. I’m not sure why but he used to race and his foster family used to get all the dogs up at 4am so maybe that’s why? Either way, it’s barking and crying and running up and down the stairs until we take him for a walk which isn’t good for the neighbours.

He also seems to have so much energy all the time and will now bark at us and bite/nibble us repeatedly in the evenings to get attention. We play with him and his ball and he now gets a 40 minute walk at lunchtime, so a total of around 2 hours walking a day with snuffle mats and playing time too. We also both work from home often so he is only left for two days a week and he seems fine on the camera. We also take him to the dog park probably once a week but he frequently hurts himself while running so we’re a bit wary.

Basically what I’m asking is, is he happy? I just want him to be happy but the barking and biting is relentless and we haven’t slept properly in weeks and I’m honestly starting to resent him. But I know he’s a good boy.

Any advice or help at all would be massively appreciated.