Males playing too rough?

Question
Okay.
So I moved into a house with my cat, Luna. This house had 3 other cats that all got along. Luna and the other female (16 year old) were actually the first ones in the house - Luna was restricted to my bedroom since she hadn't received all her vaccinations yet (she was only 6 months old)...
Around week two I saw she was losing hair on her head and her back a bit. I took her to the vet. They did a fungal culture... nothing. They checked for any kind of dermatitis... nothing. They said maybe stress. She IS a little skittish, and not altogether comfortable with loud noises and such, but I couldn't see her taking off as much hair as she was all by herself.
It's now been a month, and  think I've figured it out. It came to me when I was checking her bald(ish) spots. They had little bite marks within them. Some of them are scratches, some bites. I think the two males might be rough housing with her and biting her - because most of the bites and scratches are on her upper back and neck, which I know is a dominance thing in cats. I know they're rough housing and not fighting because I have 3 roomates (large house) and were all very light sleepers and whenever someone hisses, we hear, and it's hardly ever her (she only hisses when someone tries to eat food with her). However, I still can't understand how they're taking off patches of fur like that. I feel like  I keep exhausting all options, and I don't know what to do. I started to worry that the rest of the cats are stressing her out.
So I decded to lock her in my bedroom at night.
She cries.
She's desperate for some interaction from the other cats, since now she's used to it. And it didn't stop the rough housing either, since now she just plays with them when I'm at work and I come home and there's another patch gone.
I don't know what to do.
And I don't have the money to continually keep taking her back to the vet saying "she lost hair again" only to have them shrug and say "we don't know what to tell you".

I swear, I wish cats could talk.
All I need is the 'okay' from her that she's really not getting hurt by the rest of the cats. She seems like her usual self - she's still affectionate; if anything, she's gotten a little rougher when she and I play. She literally didn't bite me when we played up until 2 weeks ago.

Any advice at all as to what it could be, if you agree with me, or any ideas on what to do?

I appreciate anything you got...

Answer
Hi Jennifer,

Sorry it took so long to get back to you. I had problems with my Internet. It sounds like a classic case of flea allergy. You may not see them on her but the hair loss and bites sure sound like it. Get a really good flea medicine like Advantage for Cats and use it on ALL of them. See what happens in a week or two. I think you will be surprised. And since you have multiple cats I am sending you a link about how you can save money and use the dog tubes of Advantage instead. But make sure it's not the K9 Advantage. That stuff is deadly to cats.
http://www.lisaviolet.com/cathouse/advantage.html
This should work and all will be fine. Good luck.

Ciao, Karen