Can I give my dog more flea treatment?

On Sept. 17 I gave my dog flea treatment that is supposed to last a month…and last night I pulled 3 fleas off of her back to back and today she has done nothing but itch and bite herself. Is it safe to give her the next treatment before the month is up? We use First Shield. Any help is great thanks.
My vet gave me this for my dog.

I’d suggest discussing this with your vet. One approach would be to both sue a flea dip and shampoo to kill any fleas on your dog. You can then resume the spot on treatment in a proper interval.

It also sounds like you might have fleas in your home that are jumping back onto your dog. I’d thoroughly vacuum your home, wash all of your dogs belongings and use a strong disinfectant in all areas where your dog lives.