My son is almost never happy😞

Tiffany • William Dalas born September 18,2016.💙👶🏼 Teen Mom. 💕 YouTube: Dalas’ Mommy
My son is 15 weeks old today. He just seems like he is never happy. He was such a happy little guy a couple weeks ago and I don't know where that happy little man went :( Around 12 weeks old, he started to become really colicky. I have no clue why and I was always frustrated because he wouldn't stop crying. Then a week goes by of him crying so much, I get used to it and help him out as much as he will let me. From thinking his belly was hurting, being overstimulated, not being held enough, being held too much, being too hot to too cold, being sick and didn't feel well to just not knowing what was wrong. I just gave up. I took him to his pediatrician and they told me he had a stomach virus. The next week they told me he was colicky, week after that they didn't know what was wrong with him. Now I don't know what to think.
If he's not sleeping, he's fussy. If he's not fussy, he's crying. If he's not crying, he's screaming. I've only found a few ways to calm him and they aren't working... it's only temporary. Sorry this is such a long rant I just have no clue what is wrong with him and/or how to help him. He's my pride and joy and I hate getting mad and upset that he won't stop crying but I just want a solution... something that will help him feel better. I know my happy baby isn't gone. He still smiles from time to time to tell me everything's okay. I just don't know what to do anymore. I feel like such a piece of shit because I can't calm him and I feel like I've tried everything. I tell myself everyday that it's only temporary but it feels like eternity. I don't want to miss out on these moments that I know I'll regret when he's bigger....