Raw rear end

I have a small, just over one year old rescued feral kitten. I rescued her from my grandfathers (he's surrounded by farms, and therefore, feral kittens) because she was soooo small, and really not old enough to be on her own. (I would do the catch-spay-release over there, but there is a variety of issues as to why I can't).

She's a long haired cat, and when I got her initially, she was COVERED in mats. Too much hair for too little of a cat! So I got her shaved, and things seemed to clear up. As her hair has grown back in, she has managed to keep herself clean.

She had a respiratory infection that the vet put her on antibitoics for, but other than that, she's been fairly healthy, active, and eats normally.

However, about a week ago, I noticed she kinda yelped when I picked her up, but settled down once I got her in my arms. Since then, I noticed that her rear end was tender (yelped when I touched it), but it didn't look abnormal, so I chalked it up to more vigerous grooming as her hair is getting longer.

However, I got a look at her behind today, and it looks red/very irritated/kinda swollen. What is this normally a sign of? I'm thinking worms perhaps, and am going to pick up a dewormer tonight.

I would take her to the vet (and will definately if she gets worse), but I just spent $500 as another one of my cats had to have an emergency c-section (and I asked the vet to spay her while she did it).

Is there anything else it could be, or that I can do? Like I said, she's still active, still eats fine, is still cleaning herself. Her attitude hasn't changed (she's always been a bit of a ornery cat, but loves being petted if you're sitting down, and cuddles up to you if your laying down/sleeping).

Any advice is appreciated!

Impacted anal glands, perhaps?

A vet visit is the best way to get *ahem* to the bottom of things.

Worms would be one of my first guesses. Diarrhea is another one--it can often result in irritated bottoms, especially if it's ongoing. The antibiotics she's on may be the cause of the diarrhea--Spot always had that problem when on antibiotics. GingersMom's idea about impacted anal glands is also something to consider.

How long has she been on antibiotics? If the irritation started after the antibiotics, I'd suggest giving her some probiotics (plain yogurt works or there are other supplements available) to see if that helps clear it up--if not, then get her to the vet. If the irritation started before the antibiotics, I'd get her to the vet now rather than wait. Both worms and impacted anal glands will get worse and more expensive to treat the longer it takes. Either way, if she appears uncomfortable call the vet as they can give you a topical medication to help the swelling go down. Actually, I'd probably call my vet either way to confirm whether she needs to be seen immediately or whether we could wait it out.