I'm using alpha-h skin care. contains aha and glycolic acid. if i start retin-a do i discontinue aha/glycolics? can i use retin a (tretinoin) .5% once every week?

Not both together: I recommend using one or the other and not both together, as both medications have a slight exfoliating action and are likely to cause more side effects if used together. To my knowlege, Retin A (tretinoin) comes as 0.05% and that is the stronger formulation. I suggest starting with 0.0125% or 0.025% first to see how your skin responds.