I have many years of experience with generic Tretinoin cream.
For some reason 6 months has always been my 'perfection point' in regards to breakouts on tretinoin. Most don't hang around long enough to experience that. I still use it religiously only I use .1% now every few nights. And .01% around my eye area (31 and NO crows feet yet, THANK YOU TRETINOIN!)
It was almost a year in that I reached the perfection point in regards to collagen production. First it thins the hell out of your skin, then it begins causing more/tighter collagen matrixes. It also began really changing the shape of my atrophic scars as well as filling them in.
Now w if I could just stop getting cocky, going off of it, and having to redo the whole dang timeline haha. I'm destined to be on this until menopause I fear.
Hope all of you plagued with acne make tretinoin your best friend and keep it in your arsenal as a secret for life! You deserve to be acne free AND age slower than those who have blemish free skin after all of the suffering.
I use it the way you initially did but I have a fantastic tolerance now as I have used it a long time. If you aren't looking like a snake shedding it's skin, I would do a pea size for your lower face, pea size for upper region, and if you're doing your neck area, pea size there. Tretinoin DOES travel a bit under the skin. Any more than what I have said will not make it work any better/faster. But a stronger percentage may be needed if you have thicker skin, and studies say the higher percentage the faster the results. (Males and more melanin usually means thicker skin).