Okay -  these are good questions.  First of all, no one and I repeat no one should have to reapply sunscreen every two hours unless you're a professional surfer and you are spending all your time in the water being pounded by waves!!! 

Sometimes the application of too much suncreen can aggravate acne and sometimes it can even aggravate that annoying pigment after the acne (post inflammatory hyperpigmentation) IF an ingredient in the sunscreen is irritating you.    If you have an indoor job, applying sunscreen in the morning is plenty.   I tell my patients to apply it a second time in the afternoon only if they are outdoors a lot or have a long commute home with light streaming in on the driver's side.

Definately go back to your dermatologist if you are getting worse.  Occasionally Triluma can cause irritation which could make you worse.