You didn’t hurt for the first week or so because they probably put a block on you ( a little rubber ball ) and when that runs out ( usually takes about 4-5 days after surgery) the pain you thought wasn’t there shows up in spades.
And they have to push your leg beyond what you think is normal because they have to get your leg completely straightened out ( which they will do usually by putting a weight on your knee for 5-10 minutes a session) and they have to get your knee past 90degrees which is why they bend it to the point where you think it will snap.
This is all normal.I warned you this was going to be rough for the first 4-5 weeks but it will get easier but if they don’t do all this ,what you think is torture,you will end up walking with a limp because you can’t straighten out your leg.
Take your pain meds about 15-20 minutes before your session and it will help a lot.You think this is torture but I’ve been through it 3 times and I can assure you if you don’t do the rehab correctly you’ll regret it going forward.
Good luck and hope this helps.