Lactose intolerance is not a binary thing like an allergy. Instead, every human is lactose intolerant at a certain level. Meaning, there is a certain level of how much lactose you can tolerate. If you go beyond that, you will suffer the consequences.

What people usually call lactose intolerance is actually a very low lactose tolerance. Even the most lactose intolerant person will be able to tolerate very small doses of lactose without issue. It's just that these doses might be much smaller than what an average person tolerates.

So you know that you tolerate one glass of milk's worth of lactose per day. Are you planning to eat more for these three days? Then you are without promise.