Dog scratching, licking, red spots near penis. Fleas or allergies?

This could be due to an allergy, although it could also be infection or mites. + I would recommend the following:
+ Flea treatment should be prescribed by a veterinarian. It is often combined with lungworm/intestinal worm treatment. Ensure all pets in the house are up to date and treated as per the frequency recommended
+ If your parasite treatment has lapsed, or you have an infestation, treat the house with an insecticide spray such as RIP flea/Acclaim/Indorex/Frontline house spray. These sprays are toxic to cats and reptiles/fish/birds so please follow the instructions on the bottles carefully
+ If the itching continues despite the above it would be recommended to start on a hydrolysed food trial with Purina HA, Hills z/d, or Royal Canin Anallergenic for 6-8weeks. This must be fed strictly and exclusively to see if it works, which means absolutely no treats or human foods otherwise the results are inconclusive
+ If all of this makes no difference then you will need to discuss investigations into environmental allergies with your vet, or be referred to a dermatologist
+ If a food allergy is ruled out then consider a skin diet (Royal Canin skin/Hills Derm Defence) or a skin supplement such as Yuderm, to help boost the skin barrier and prevent/reduce flare ups in the future. The following products can be found online and can be tried as a first line approach: Douxo PS Calm shampoo, Essential 6 spot on by dermoscent, Krillex Krill oil chews.