What is the man’s problem?

M: Melanie, this dip is really good. Thank you for bringing a dairy-free version. At the last office potluck party, I accidentally ate some that had cheese in it, and I had a stomachache for the rest of the afternoon.
W: Matt, I’m afraid that the dip I made hasn’t been put out yet. Cheryl put it in the fridge because she thought that there was enough food out already, and more people from accounting will be coming later.
M: Okay. I will stop eating this one. Perhaps it won’t be so bad. I only ate about two or three mouthfuls.
W: Have you tried that new medicine for people who can’t digest dairy foods? My sister takes it, and she says it’s very effective. You can buy some from the drugstore downstairs.