Sorry to hear about your dog.
Did the vet tell you the dosage? It sounds like he is being a bit caviler about giving a dog aspirin!
"the general recommended dosage of aspirin for dogs is around 5-10mg for every 1lb of your dog’s body weight,
given once every 12 hours. Again, you must calculate the exact dosage your dog needs based on their weight,
because dogs of different size and weights could require very different aspirin dosages.
Let your veterinarian take care of calculating this part, as any mistakes in giving your dog an overdose of aspirin will put them at serious risk of damaging their organs."
"*Aspirin should not be given to dogs which suffer from the following conditions: Arthritis – because when used for long periods of time,
aspirin will damage your dog’s cartilage and make their arthritis problem much more complicated than it already is.
*Do not give it to your dog for more than 5 days in a row without the permission of your veterinarian or an animal care professional, as un-monitored long term
consumption of aspirin in dogs can lead to very negative repercussions
There are natural herbals like the Tumeric (llomabardo mentioned) and many other herbals that would be a MUCH better choice! FYI: Tumeric is also called Curcumin (Curcuma Longa).
These are two that I am using right now (among others that I rotate with)....one in the morning and one at nite:
(human anti-inflammatory): http://www.amazon.com/New-Chapter-Zyflamend-Wholebody-Turmeric/dp/B0009F3RW4/ref=sr_1_1?s=hpc&ie=UTF8&qid=1452776502&sr=1-1&keywords=zyflamend
Canine "Activ": Info: Canine Activ ? Safe alternative to ibuprofen & NSAIDs