Is he itching a lot?
Any loss of hair or bald spots as a result?
Is he on flea preventative?
Any change in diet or environment such as moving?
What breed is your dog?
The rash sounds like a skin dermatitis such as staph dermatitis or yeast dermatitis. These skin conditions are generally seen with allergies. Staph usually occurs on the lower regions of your pet and tends to have small pimple type bumps. Shampoo containing Chlorhexiderm and/or Oatmeal can help with this condition. Yeast typically shows as a greasy area that has a sweet musty odor. Sometimes the skin can become inflamed, darker and thickened due to itching. Yeast likes areas such as between toes, armpits and ears. Selsun Blue Shampoo can help with Yeast dermatitis. When shampooing, lather and leave on 15 minutes before rinsing. These shampoos are not meant to be a cure, just a relief until your pet can see a Vet. Benadryl can be given to your dog, the dose is up to 2mg per pound every 8 hours for itching due to allergies. You can read about allergies here: http://www.nhahonline.vetsuite.com/Templates/ContentPages/Articles/ViewArticleContent.aspx?Id=864 http://www.lbah.com/allergy.htm
Here is a site that goes over itching in dogs.http://www.petplace.com/dogs/itch-itch-itch-when-your-dog-can-t-stop-scratching/page1.aspx
Some dogs do suffer from dry skin and this would look a lot like dandruff. Fish oil capsules can help with dry skins and improve the coat as well. If your dog is drinking more and urinating more than normal, that might indicate a urinary tract infection.
Common symptoms of a urinary tract infection are frequent urination, dribbling urine, blood in the urine, squatting frequently to urinate, strong odor to the urine, inappropriate urination and straining to urinate as well as an increase in fluid intake.
A dog with a UTI does not always show all the symptoms and typically displays 2 or 3. I believe you need to have your Vet check your dog out so it can get medication for the problem if your dog is displaying 2 or more of the above symptoms..
Other causes for increased thirst and frequent urination include kidney failure, diabetes mellitus, cushing, a uterine infection (called pyometra), and liver disease to name a few. You can read about this here: http://www.petplace.com/dogs/polydipsia-and-polyuria-in-dogs/page1.aspx I hope this information is helpful to you.
You can certainly try the shampoo and over the counter medicine for yeast infections containing miconazole will often work on dermatitis.
I can't recommend that you use an antibiotic for a possible UTI without consulting your vet. However, two that are commonly used are cephalexin (Keflex) and Enrofloxacin (Baytril. You can read about Keflex and dosages here: http://www.petplace.com/drug-library/cephalexin-keflex/page1.aspx
You can read about Baytril and dosages here: http://www.petplace.com/drug-library/enrofloxacin-baytril/page1.aspx
This site discusses UTI's and various medications used for treatments.http://www.vin.com/proceedings/Proceedings.plx?CID=WSAVA2003&PID=6538&O=Generic
I do have to tell you that you should have your dog seen by a Vet for any UTI and should not administer any prescription medication without notifying your vet first.
I do not know of free clinics, but the following organizations may help financially.
Care Credit http://www.carecredit.com Quick application and approval for care credit card. You can sometimes apply and get approval while you are at the vet office.
American Animal Hospital Association http://www.aahahelpingpets.org/home/ Helps animals that have been abandoned or if the owner is having financial hardships
Angels 4 Animals http://www.Angels4Animals.org This organization offers financial aid or treatment to those pets and owners in need.
God's Creatures Ministry http://www.all-creatures.org/gcm/help-cf.html Help pay Vet bills for those that need help
The Pet Fund http://thepetfund.com/ Helps provide emergency vet care to those in need.