Hubby had the same with his initial plastic cages. They are brilliant for getting into denial but once you’ve figured out what size works for you and got used to it then definitely worth trying some metal ones which tend to be comfier for longer term wear.
So, ways to fix it in the mean time. Firstly your cock will get used to it (says our experience and what I’ve read) – it’s just used to being able to get hard at night with no problem and so does. This then pulls the ring on your balls till it hurts enough to wake you up.
So, ways to fix this, get a SMALLER cage, yep, with no room to grow at all it gets less painful as with a bit of a gap your erection seems to ‘build up steam’ and so try to go full hard on. With nowhere to go it seems to not do this so much.
Secondly, good silicon lube to stop the ring chaffing, which is what hurts.
Then thirdly it’s just time for your body to get used to it, and it will. Hubby barely wakes up any more now he has a nice tight metal cage and has adjusted.