Which derma caps for my dog ?

I have a 3 yr old male lab. He was itchy, licking , biting himself and had little circular sores on him and was moulting badly. On visit to the vet he said he has a skin allergie / condition prob dermatitus brought on by the flees he thinks. The treatment was 1 shot and clyndacil for 4 weeks along with strong hold flee treatment. My previous vet advised frontline every 6 weeks which is why my current, new vet said my lab got flees back because apparently frontline should have been applied every 4 weeks and 2 pipets to be used because he is a big dog. I am so mad that my dog has suffered because of the wrong advise of my previous vet. Now to try to put things right I have changed his food to hypoallergenic dry and wet food. I shall be applying strong hold every 30 days and give him sardines or olive oil every other day. His coat is dry, flaky and dull due to his recent condition which I dont want to return. I have heard that Derma Caps ES, Denes greenleaf caps and benadryl or cortisone antihistamines are also recommended to give him each day along with omega 3 & 6. However I dont want him to overdose and I think omega 3 & 6 are in the derma caps, am I right ???obviously I am going to ask the vet but just wondered if anyone has had these problems, can recommend these medications or not, any advise ??????????????