11 month old Weimaraner with bumps on back

Question
In early July, our 10 month old Weimaraner had a few raised bumps near neck, shoulder area that stayed for a few days.  We had been on a walk in a buggy forest area and had seen flies on her a week or so before that.  I assumed she had bug bites.  I checked her for fleas and she was clean but decided to treat her with Frontline Top spot that day.  Seemed like more bumps popped out over night so gave her a bath the next day with a gently shampoo in case that irratated her more (Zyomox shampoo for itchy skin).  Vet put her on Cephaflexin (500mg 3x day) but bumps waxed and waned and after 1 week, I was told to discontinue as not an infection but more like an allergy.  We were given generic Zyrtec to give her once a day.  After no improvement and bumps worsened after stopping Cephaflexin, ran her back in and she was put on short course of Predisone (10mg 2xday for 3 days, 10mg 1xday for 3 days and then 10mg every other for 3 days.  Again, bumps waxed and waned but never went away or new ones popped up.  Call to vet and said to finish Pred and then restart the Cephaflexin again.  She seemed to be improving and almost gone after being on Cepha... for 5 days, then over weekend, bumps started again.  The bumps are small and some are pale pink no ulceration, some red and larger with dried blood in middle where it looks like scratched open and a few look like they are coming to a head (white/yellow fluid right under skin).  She seemed more itchier when they first started than now, but the pimples will pop up here and there in a few hours.  She is 47lbs, indoor dog, does go to daycare once or twice a week and walks in mostly neighborhood area.  The bumps are only on her back, top near shoulder and sides.  No redness on feet, nothing on belly, armpits where I would think of food or contact allergy.  She is on and has been on high quality kibble (Taste of Wild) but am trying a Fish based kibble now that not going away (Orijen fish).  Up until early July, she has had no skin issues and no food issues.

Answer
Did your vet do a deep skin scraping to check for demodex mange? To treat a bacterial skin infection, it may take 3-4 weeks of continuous antibiotic therapy rather than intermittent.  If the steroids did not really help, then there may be a skin parasite or foreign material in the skin in that area.  I would recommend having her dipped for mange to rule that out.  If these still persist after all of the treatments you have done, a skin biopsy may be needed to see what is going on microscopically in the skin.