I'm not sure how your doctor told you to use Retin A so these suggestions might help:
1 - wash face with gentle cleanser and wait at least 20 mintues before applying Retin A
2 - apply only a pea size amount all over face - avoid nostril and eye areas
3 - apply every other day to start
4 - make sure you use sunscreen or makeup with sunscreen as your face will be very sensitive to the sun and sunburn easily
5 - do not wax anywhere you apply Retin A. If you do, it will burn and you will look like you have a rug burn on the waxed area.
Once your skin is comfortable with the Retin A every other day - might take 4+ weeks - apply the Retin A every day.
Retin A's active ingredient is Tretinoin. Mixing the wrong ingredient with the Tretinoin can make it ineffective.
Anytime you want to use a moisturizer or other product with the Retin A, run it by the pharmacist.
They will let you know if you can use the two together or use them several hours apart. Retin A at bedtime and Obaji in the morning.
I've been using Retin A about 20 years. I went up to a higher strength last year and I'm still getting use to it.
Whenever my face starts to get irritated - red, sore - I don't use the retin a for a few days. And I apply a very thin layer of Vaseline on sore areas and my face generally feels better the next day.