If it was from your vet, then it was probably one of the two I mentioned as those are the popular choices since they do work well.
It could be a few different things. First thing is to definitely rule out fleas. You should at least explore the possibility of fleas by examining your dog’s skin especially around the rump area under a bright light. Fleas are fast and are a reddish brown color so you have to look closely. Frequently you will only see flea dirt (feces). If you find fleas dirt or what you think is flea dirt, get a moist white paper towel and rub it on the area. If it turns reddish color then it most likely your dog has fleas. A flea comb or lice comb run through the area may capture a live flea as well.
If your dog has fles, your first step will be getting your dog on frontline or advantage to get the fleas off of your dog. If that is not an option, washing your dog in dawn dishwashing liquid, leaving the lather on for 15 minutes before rinsing will kill the fleas. The second step will be ridding the environment of them.
There are quite a few house sprays available to control fleas in the house. I've used Flea Stop but any that include a growth inhibitor should do the job pretty well. Cutting a piece from a flea collar and adding it to your vacuum bag will kill any fleas that you vacuum up and prevent them from escaping back into the house. Vaccum every day for at least a month to get all the fleas and eggs out of the carpets.
You can also treat the yard if you wish with Diatomaceous earth, which helps kill them in the yard without poisons. This can also be used in carpets as well. You can read more about that here.
Fleas do not like a wet environment so frequent watering of the lawn can also make it inhospitable to fleas as well.
I'm going to discuss hair loss now and then talk about your dog's losing clumps of hair. there are many conditions that can cause a dog to experience hair loss 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:
Here is two on Mange.
Hypothyroidism and cushing on these pages:
You can read up on allergies here:
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:
Some treatment methods for this are discussed on the following site. You might want to discuss this possibility with your vet.
If you are seeing bald areas then you should look into one of the above reasons including a flea allergy condition. However, if it is is clumps of hair coming out but still not leaving bare areas, then it might be normal shedding. It is the time of year when dogs will lose their winter coats. My dogs are rotties and I still take grocery bags of hair off of them in the spring when they lose their winter coat. If this is the case, you will want to get a good shedding tool or brush often to remove the old hair.
I hope this information is helpful.