Guinea pig shedding

Question
I have two female guinea pigs and I have noticed a lot of shedding, and now dandruff on their fur. At first I wasn't to worried with just a little shedding, I thought it could be seasonal. But its getting worse and worse, and now the dandruff, I am thinking it could be mites, but I would like to avoid a vet trip if possible, because there isn't a small animal vet close to my town. Would a canine, or another vet give me some ivermectin, and would that be ok to use, for not just mites but whatever the problem is with the shedding? If not is there another medication I could order online?
Thank you in advance for your help!

Answer
Dear Adria
Check through the fur by sweeping it up with your fingers against the growth and see if you can spot anything first
If it is greasy to the touch means it could be a fungal infection.
Try bathing them both in SELSUN shampoo twice a week for 2 weeks.
If after this time it has not cleared up a little then it could be parasitic in which case your vet will prescribe a suitable medication. Try the shampoo first tho and get back to me if you need more help