My lab is not feeling good

My active 8 year old lab is just laying around and not eating she did drink some water. she is having a hard time having a bowel movement and at one time when she got up she wouldn't use her right foot. I know I need to take her to the vet but wondering if anyone could give me an idea what could be wrong

OO gosh I'm going through the same thing with my cat. She's only 1 though. She hasnt ate anything in a little over a week I dont even know how shes still alive she wont drink I have to force water down her throat. Shes reall weak too cant walk right. I asked peoples adive on my cat they suggested maybe she has leukemia or kidney disease, and it sucked because I had no money to take her to the vet, but I got good news today that my boyfriends job at a VET said he can bring her in 2 morrow so I hope it will go well if it's something too dangerous I guess they'll have to put her to sleep.! :*( Good luck!!!