Hi Sir or Madam,
I don't quite understand why your vet would give your dog aspirin for itching. Aspirin is normally used for minor pain relief and only used for a couple of days. The areas you indicate are the ones where we usually see flea activity. I would start flea preventative immediately. Now there are a few things you can do for bald areas you are seeing now if they are a result of a flea allergy. You can trim back the hair and clean with a good antibacterial soap and then you can use witch hazel or neosporin on the bare areas. I have also used vasoline with a little flea dip mixed in and used that on these areas with good results as well. I usually see hair regrowth in about a week of twice daily use. If a dog is allergic to fleas, a single bite can set off the allergic reaction which leads to itching and hair loss.
Now there are other causes of hair loss that I want to go over with you including ringworm, mange, hypothyroidism, cushing disease and allergies.
Ringworm can have a scaly reddish rash around the edges of the bare patches though there can be a rash in the bare area as well. Any over the counter antifungal cream for ringworm will work on this. The cream should be applied to an area slightly larger and for about a week after it appears to have cleared up. There are two types of mange and mange is actually caused by mites. Usually hair loss starts in specific areas of the body before spreading to other areas. Allergies are a frequent cause of scratching and hair loss and an be caused by many different things. Treating any problem without knowing for sure what it is causes a delay in the treatment of the real problem if your first guess is wrong. I really suggest you have your Vet examine the areas and diagnose this. Below are websites that will go into more detail on these conditions.
Here is a website on Ringworm:http://www.marvistavet.com/html/body_ringworm.html
Here is two on Mange.http://www.marvistavet.com/html/body_demodectic_mange.html http://www.marvistavet.com/html/body_sarcoptic_mange.html
Hypothyroidism and cushing on these pages:http://www.petplace.com/dogs/hypothyroidism-in-dogs/page1.aspx http://www.petplace.com/dogs/hyperadrenocorticism-cushing-s-syndrome-in-dogs/page1.aspx
You can read up on allergies here:http://www.nhahonline.vetsuite.com/Templates/ContentPages/Articles/ViewArticleContent.aspx?Id=864 http://www.lbah.com/allergy.htm
If you suspect an allergy condition is to blame, you can give your dog Benadryl up to 2mg per pound every 8 hours.
There might be a secondary skin condition in addition to the allergy such as staph dermatitis or yeast dermatitis. 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 though it does not cure the allergy. 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.
There is also a condition called alopecia which is basically hair loss. You can read all about it in this article: http://www.dvmnewsmagazine.com/dvm/article/articleDetail.jsp?id=7250
Some treatment methods for this are discussed on the following site. You might want to discuss this possibility with your vet. http://www.vin.com/proceedings/Proceedings.plx?CID=WSAVA2004&PID=8629&O=Generic
You could also elect to have allergy testing done to determine the cause as well. Once the allergen is determined, it can be avoided or desensitizing shots can be given to prevent the reaction.
I hope this information is helpful.