I have tiny bumps and redness on forehead. Some have white dots in them. I took antibiotics 5x this year, and was using retin a (tretinoin) - could it be yeast?

It may be. This could be standard acne that is not responding but at times a secondary yeast infection and develop. It would be ok to use an over the counter anti-fungal cream such as clotimazole for 10 days and see if there is improvemnt.
Comedones. Most likely comedones (plugged oil glands), but could also be tiny epidermal cysts called milia. Unlikely to be yeast. A dermatologist will be able to tell you exactly what they are, and what you can do to get rid of them.