2-yr-old Chihuahua not eating and don't poop

Recently my dog remy, a 2-yr old chihuahua stopped pooping for her daily walk. then i discovered that the left side of her butt is swelling and all red. i took her to the vet and they gave her pills, she never ate them even i put them in water. she haven't eaten for 3 days and im super worried about her, now all she does all day is lying on the wood floor or her mat. and then i found out that the part under her tail, where she urinates and do her bussiness, is red and swelling and suppurate as well. i tried putting ice on it and she whimpers with pain. also, i remembered that she always wipes her butt on the carpet, i thought it was normal for dogs to do that. could that be related to her issue now? WOULD SOMEONE PLEASE PLEASE PLEASE tell me a way to help her and help me with whatever information that relates to this. THANK YOU SO MUCH!!!

[lindapalm]

If your dog didn't take the medication your vet prescribed, I would call him and let him know.  She has to eat food, and especially drink water, and soon. She is too small to go for very long  the way she is.

[Misfits4Me]

This is what your dealing with & it's common!!!!....I have posted a thread that will explain it...You need to see another Vet ASAP.....Pills won't work if you put them in water...She won't drink enough to get the full benefit of the meds....You need to use small pieces of cheese or meat or peanut butter to wrap your pills in.....A dog this small cannot go without food or water for more than 2 days....dehydration alone can be fatal...Again, you must see your Vet tomorrow......Here's the link:

http://www.medhelp.org/posts/Dogs/Something-going-on-with-my-dogs-butt/show/1794811