Hair Loss Loosing hair what do I do?

Hi my Coco is loosing hair and from what I've read that is not normal, she'd lost a clump about half the size of my pinky a couple days ago and this morning I found three clumps of hair. She seems to be eating fine, I noticed when she's not eating she scratches but I not sure if its excessive scratching ( as I've only had her for 3 weeks). So I'm thinking it might be mites, do I just treat her with invermectin( think that's what it's called) can I treat her myself or does she need a vet? Can I even buy the treatment my self? Or could there be another reason for her hair loss? She has calcium showing in her pee but not sure if that's a factor... Sorry I'm kind of a paranoid new mom