sleep regression?

My son has been having trouble sleeping since a week before he turned 4 months, he'd cry every time he was put to sleep. He's now a week away from 5 months and still cries every time he's put to sleep, but the last couple of days he won't stay asleep longer than 20 minutes during the day. He sleeps a total of 2-3 hours during the day. I think it's making him over tired because he's been crying a lot more, but he just won't stay asleep. Anyone experience this before? Any advice?