My son is 4 months old. For the last 2 days he's been cring every 10 minuets like he's in pain.?

I took him to the doctors and she said he's fine. He has never done this before. So I called the doctor back today and she said that babies start to fuss more at this age. JgggBut its not fussy its like he burts out into tears and screams. He had fallen off the bed which is a basic twin bejd but the doctor said that he'd be fine from that by now. He also has had really stinky gas but hasn't pooped in 3 days, but that's normal for him. I don't know what it could be. Please help, I'm worried about him!!