Retinol for men aged 20

I am beginning to get dark acne if that makes sense im clueless basically when it comes to skincare and turn 20 soon I'm a male. Recently I haven't got normal acne like I used to I had semi clear skin for a few months but now my acne has flared up due to a mixture of a poor diet, lots of sugar and chocolate and lack of sleep. The spots and pimples have gone down the past few weeks but now I have what appears to be dark blemishes on my face not spots but like dark marks that look like spots if that makes sense. My current routine is just cleansing twice a day with just water and apply la Roche posay SPF in the morning and then my duac prescription at night but on alternate nights I'll just apply effaclar duo. I've now invested in the la Roche posay cleanser aswel as I think cleansing may be important but I'm thinking of incorporating retinol into my routine so perhaps I can use duac some nights then retinol on alternate nights and just use the effaclar duo in the morning before applying my SPF? But in terms of retinol I don't know much about it what strength should I start with and what brand should I go with?