Sleeping battle

My husband and I are first time parents. My son is 6 months old, every single night is a two hour battle. He screams himself to sleep. The frustration is really setting in and we need help! Why is this happening? We thought maybe teething, we have tried rings, Tylenol, and orajel, still no luck. We thought maybe ear infection but he just had his 6 month apt, and they were fine. Next we thought maybe he's just simply not sleepy. We have kept him awake since 3 every day, still two hours of hell. Anyone have any tips? Please help, I hate seeing him so upset but I'm at a loss of what to do :(