EBF to formula?

My EBF baby will be 15 weeks this week. He has been fussy and cranky since about 1 week. It hasn’t eased up and he is just upset all the time. He is definitely gassy and had colic. My MIL suggested trying to see if formula helps him. So we are thinking about supplementing with formula a little to see if it helps. Has anyone done this and had positive changes? Negative changes? No changes? TIA.