I'll assume your talking about a full-size M&P since you didn't say "compact."
First change would be to go with an IWB holster. The gun needs to be held closer to your body.
You may need pants 1" larger in the waist to do this relatively comfortably if your pants are on the snug side, or "fit" without a handgun stuffed in them to begin with.
"Under your shirt" - t-shirt? tailored/loose shirt? Hawaiian shirt?
First change would be to go with an IWB holster. The gun needs to be held closer to your body.
You may need pants 1" larger in the waist to do this relatively comfortably if your pants are on the snug side, or "fit" without a handgun stuffed in them to begin with.
"Under your shirt" - t-shirt? tailored/loose shirt? Hawaiian shirt?