Every labrador owner will have had the same thoughts and moments (months) when they feel like you do OP.
Bad news is that I think 9 months + for a few months is the worst age for behaviour. Good news is that it will pass!
Agree with getting a good gun dog trainer on board.
The trainer can help with settle , impulse control and ideas to help mentally tire out your lab.
The trouble with young labs is that their brain capacity is short and when they get tired they turn into zoomie humpy crazies.
If they dont get enough mental stimulation they also turn into zoomie humpy crazies.
I would not rush to get him castrated yet. It wont make a lot of difference to his behaviour and can have long term issues if done to early.
I find that when labs stop chewing and biting when their teeth come in they transfer the behaviour to humping. Keep things they can hump out of their way, cushions etc.
Give your dog a nice walk, food etc and then encourage quiet chill out time. Get into the habit of this. The walks may be short and the quiet intervals may be short but it is a habit that your dog will recognise and both will become longer and it will get easier.
Keep up the training, dont expect too much new learning in this time period but carry on reinforcing what they do know. Keep the environments calm.
This too will pass
You are not letting your dog down they are being a twatador and will soon become a loving loyal labrador. Hang on in there