@MikeMason-- I think lisinopril can cause weight gain if the fatigue is very bad. Fatigue is a common side effect of lisinopril but it affects some people more than others. I can easily see how someone who is tired all the time might be inclined to eat more and exercise less.
Do you think this is what happened to you?
Some drugs really do cause weight gain as a side effect, like anti-depressants. But blood pressure medications usually don't cause weight gain. They can cause edema which looks like weight gain, but you already said that you don't have edema.