Is my cat ill? please help?

I have a 8 or 9 year old pure bred turkish van cat. her body is like 98% white except the top of her head, her ears, and her tail. I groom her once a month brushing her and her fur is always pure white. I have 4 cats and all but 1 are overweight(not by too much). My turkish van likes to stuff her face and then occasionally throws it back up because she eats too fast. Recently I noticed her throwing up a little more often then usual but I didn't think it was too much concern. Now I notice her having diarrhea for the last 3ish days, to where it sticks to the fur and smells terrible. I have given her a bath yesterday to clean her and today its back stuck to her tail. Her appetite is just fine as well as her water consumption and she is still acting normal. I noticed a scab or a cut on the tip of her nose for the last week but her and my other cat play rough sometimes and shes had that once before so again I ignored it. Now tonight she was laying on my bed and i was scratching her back and looking threw her hair and noticed like black dirt that appears like flea dirt. All 4 of my cats are indoors and never have been outside in their lives(well not since i've had them anyway for the last 8-12 years) Its sporatic throughout her hair but not a lot of it either. Then I seen a bug crawling threw her hair that was a little bigger then a flea and didn't look like a flea to me but I ended up killing it. Now I got paranoid and now I think my mind is playing tricks on me thinking shes losing a little weight and looks thinner then normal(mind you she has very fluffy hair so it's hard to tell anyway and she already is overweight). I checked her back end and do not see any signs of worms but i thought maybe that could be it and i am unsure of where these lil black dirt pieces that look like flea dirt are coming from. I am struggling terrible with money and really cannot afford the vet but if this sounds very serious to someone then I will obviously make the appointment. I did change their food about 4-5 days ago because of her throwing up more often I umed it was the food. I BELIEVE the diarrhea started after changing the food but I could be wrong. The flea dirt is what is bothering me thinking it could have something to do with that. I have 3 other cats with no signs of fleas or flea dirt, as well as 2 dogs. Her gums look pink in color she doesn't have thick saliva and doesn't appear dehydrated especially since she is drinking water. She still is purring just as often and still follows me around. I tried giving her white rice and she will not eat it, even putting some chicken broth on it to stop the diarrhea, yet she would eat anything else I put in front of her face if it was offered. I do have an indoor rabbit and she tends to get into the timothy hay if it falls out of the cage and eats it and she used to throw it back up. When she's been vomiting I have NOT seen any timothy hay but I'm not sure if that could be the problem too but she would not of been able to come across any of that lately but I don't know if it could be from weeks ago when she did eat a piece. Does anyone else have suggestions to stop diarrhea, does boiled chicken stop it? Or just white rice? What do you suggest to get this flea dirt out of her long hair? She doesn't mind bathes but are their powders to get rid of it and is it ok for a 9 year old cat?