Constipation?

My poor LO has been fussing, crying, and squirming since 9pm last night. He was able to sleep ok but woke way more frequently than normal. It seemed he was having gas pain but nothing helped. I tried his gas drops, bicycling his legs, I even tried sticking the thermometer up his bum this morning. Nothing. He also hasn't pooed in a long time (not since around 7pm last night). He's breastfed and over 2 months old. He normally has about 4-6 poos per day. How do I know if he's constipated? It's not colic. He is consolable. He just looks like he's in discomfort; arching his back and crying.