Cannot sleep because of random erections in the middle of the night lasting hours. usually around 3 or 4 am - 5 or 6 am. solutions ?

That means: That the balance between rem (rapid eye movement) and deep sleep is abnormal. A sleep cycle lasts abouf 90 minutes and rem should be about 10 mins within that cycle. Rem is also known as "active sleep" and erections are normal in this part of the cycle. Your rem phase is exaggerated. It could be as simple as poor diet affecting brain controls.

That is normal: I would ask if you are eating or drinking anything past 7pm? (either hot or cold drinks). Avoid that late evening. How is general mood? Have you gained or lost weight? Being down might also be a reason. Evening exercise outdoors/shower might be key to restful sleep.