Retinoid side effects. Or lotion. ?

I consulted dermatologist for my acne scar in nov. 2016. He advised to apply trunex(retin a micro 0.04%) on the scar with face guard sunscreen. I applied trunex on both cheeks. On right cheek I applied sunscreen regularly with trunex. But on left cheek I did not apply sunscreen when I applied trunex on 18,19& 20 nov. 2016. On 28 nov. 2016 my left cheek turned purple due to sunlight (trunex side effect). Then dermatologist prescribed me lutica(a steroid) . I applied it on that patch on left cheek for 7 days. The patch got better. I did not apply trunex from the last 3 months on my left cheek but still the left cheek becomes dry and red if I stop applying moisturiser on it. Presently I am applying physio gel AI body lotion and UV2IR sunscreen on my left cheek as suggested by dermatologist. But the dry ness and redness is still there and not going permanently. Should I use another sunscreen or lotion.?