What does my horse have? Is it real bad?

Okay, so I have a mare that was never ever ridden before I bought her, my trainer saw her last year (because she lived about a block away and he and her old owners are good friends) he says that when he saw her last summer that he didn't see her with what she has now. She has the bald spots, she's loosing a lot of hair, he says it's a fungus but what kind? There are only two major bald spots, the rest are bald specks... But they are still all over her, so it looks real bad. I don't think she's sick,because I rode her yesterday and I've been entering her in a summer series, and she wanted to run, she was feeling real good and she worked well for me... But what does she have? I bought her in November, and it started as soon as summer started... I started using Fungal Shampoo, and it was working quite well in the two days that I used it! But then my family and I left for vacation for 6 days, and I came back and it looked real bad, that's when the two actual bald spots formed... Before that it was just bald specks.... Thanks SO much!