Can benadryl be given along with clavamox to a dog ?

Generally speaking yes. Diphenhydramine (Benadryl) is exceptionally safe for dogs; however, there are a certain number of serious precautions:

•Diphenhydramine should not be administered to dogs with certain conditions: cardiovascular disease, glaucoma, prostatic disease, and hyperthyroidism.
•Diphenhydramine (Benadryl) may not be appropriate for a puppy. If you do have a puppy, please be sure to consult with your veterinarian first.
•Only the pure med is safe for dogs, where the active ingredient is only Diphenhydramine. The Decongestant or Colds/Sinus versions aren't acceptable. Re-read this paragraph again, it is critical.
•Liquid Benadryl is high in alcohol content and is not safe for most animals.
•Children's Benadryl may be alcohol and sugar free; however, it contains sodium, and this could be detrimental to dogs with certain health concerns.
•It shouldn't be used simultaneously with decongestants and painkillers. It can also interact with other medicines, and possibly be fatal. Should your pet be taking any other types of medication - it's important that you first ask your veterinarian about using Benadryl. Generally, Diphenhydramine is considered safe for your pet when taking flea and heartworm tablets, as well as steroids.
•It's extremely important that the prescribed dosage is not exceeded.

There're 2 ways for determining the proper dosage when administering Benadryl to a pet:

1. Benadryl (Diphenhydramine) is administered at a dosage of 1 milligram per 1 pound of the animal's weight 3 times per day (i.e. every 8 hrs). An example: a 30 lb dog should be given 30 mg of this medication three times per day.

2. Dogs are categorized by three weight class categories; the med is taken 3 times daily, every 8 hours:
•30 pounds and under pets: 10mg
•30-50 pound pets: 25 mg
•50 pounds and over pets: 50mg

As you can see, the dosage of Diphenhydramine depends on the animal's weight, and the aforementioned are just the general recommendations.

You need to see or talk to your veterinarian. Should your current financial situation not permit a paid visit to your vet, you should still be able to get free advice by phone. Best wishes.