It is really difficult to determine the cause of the bumps without examining him as there are various things that can lead to them. Superficial skin infections caused by either bacterial or yeast organisms are a common cause, and they may or may not lead to itching. Dogs that are allergic to things in the environment (like molds, pollen, etc) can develop bumps on the skin, but these are almost always itchy. The benadryl would most likely only help to resolve them if they were due to allergic dermatitis, and even then, antihistamines don't always work. The dose you gave him was on the lower end however and you could easily double what you gave him (up to 50 mg twice a day). With a concurrent itch factor though, I am not too convinced these bumps are related to an allergy.
Some dogs will get plugged hair follicles or comedones and that can lead to a "bump". Of course, there are also skin masses that can grow anywhere on a dog's body, but I would be surprised to see them all occur so acutely over the past week.
Without knowing the cause, it is hard to say what would help, but there are a few things that might that certainly won't hurt. An antiseptic shampoo from the pet store can decrease the bacteria and yeast if they are present. I like the product called Hexedene® because it contains chlorhexidine which is effective on bacteria and yeast. Bathing with appropriate veterinary shampoos will not dry out the skin and follow up with a humectant like Humilac® to protect skin moisture: Humilac There is also a "leave-on" product called Resi-chlor® with similar ingredients that can be used to decrease bacteria and yeast in between shampoos.
Adding an omega 3 fish oil may help, especially if her skin is dry. There are literally hundreds on the market. The active ingredient of fish oil for humans and for dogs is EPA (Eicosapentaenoic Acid) and DHA (Docosahexaenoic Acid). The dose recommendations are 180mg EPA and 120 mg DHA per 10 lbs body weight daily.
There is a large range of safety and it doesn't have to be that amount exactly but this gives you some guidelines. You just want to make sure you are seeing those on the label as an ingredient and not just the words "fish oil" as these are the important part of the fish oil and not all fish oil capsules have them in it, especially the cheaper ones.
If the above suggestions are not helping or if the skin condition is getting worse, it would be advisable to have her examined by your veterinarian. I hope this is helpful. If you would like any additional information or have additional questions please don't hesitate to ask!