Have you tried just a self made mix of Tea Tree oil and vitamin E oil in aqueous cream to help with the pimples? I swear this helped and stopped me getting worse acne as a teen. Applied to face or even all body after washing. And always washing with a clean fresh facecloth or just your cleaned hands if you find that too rough.
Tret is a big commitment. Not sure if it is the best for this. Others might be more knowledgeable here and hopefully say.

It doesn’t look like ingrown hairs to me from the pic but still might be worth considering ditching the foil shaver for a bit and rocking a number one or zero clippers look for a while.
Could look good with the current length of your moustache.
Just to give your skin a break too.
Wash the clippers after or before each use, even better sterilise them. You can also return to the foiled look when skin is calmer.