HELP! baby gassy at night- need advice and sleep!

My 3wo is super gassy only at night and we are getting zero sleep between the feedings and then dealing with the gas. I started pumping and giving him bottles with half breastmilk/half formula since I'm not producing enough. I use the gas drops before each bottle but doesn't seem to do much. Could it be a dairy sensitivity? He's fine during the day so I didn't think it was a formula or dairy issue but not sure. Help!!