Back in the 90's, they made an OTC called "heads up" was the active ingredient ephedrine? Isn't that found in some antihistamines?

Not that I can find. Why do you ask this?

My friend and I used to work 3rd shift at a factory, and she found taking them kept her focused and alert, she has concentration problems, and her doctor just poo-poos her

Okay.

Find a different doctor. Until you're satisfied with the answer. Though if you go through more then three doctors who say the same thing... maybe there isn't a problem.