Why is my 6 month old crying so much?

He has slept threw the night since i brought him home. But for the past 2 weeks he wakes up SCREAMING every 30 mins. He has had constipation issues since he was born, But i'm still having to help him got to the bathroom every day. I have tried everything formula,juice,fruits,over the counter meds,and suppositories. The Dr. hasn't suggested anything else. Keeps saying he will hopefully grow out of it. But I'm Sooo tired ! I have a 2 yr old as well and he wakes him up every A.M way to early because his cries are so loud ! My nerves are on edge because every time he wakes up, I'm just falling into a deep sleep & it scares the crap out of me. I tried having my husband get up with him at night, Because he works nights and sleeps in late. But he doesn't get up just lets him cry & sleeps threw it. Any advice would be helpful, I feel so bad for my Little guy, Can't figure it out or fix it. Ps. He also does this during nap time & Cries all day. I've tried keeping him up during the day to make sure he wasn't getting to much sleep, But that hasn't helped either.