Thank you so much for your advice. She has only been on the medication for a day and a half and i'm already freaking out. I'm just really worried because I'm not sure how old she is. My mom loves dachshunds (she has 7) and Dolly ran out in front of her on a very stormy day about three years ago and almost got ran over. She had no coller and there were no houses within miles so my mom decided to take her home. She has been so spoiled and we love her a lot. We are all hopeing that it won't be cancer. She has had really bad breath since we found her but I never really thought too much about it. I will definitely be informing the vet of that when we take her back. Thanks again! I'll give an update as soon as we find out something!
Sure, it's possible that it's a cancerous growth, but the only way to make certain is to have it biopsied. If the antibiotics don't help in a few more days, ask your vet about having the biopsy done. It may just be a benign cyst, but may need to be surgically removed in either case.
Did you notice any decrease in the sneezing once you got the benadryl on board?
The bad breath actually concerns me more than the lump. Can you tell if she has puffy red gums (gingivitis) or a lot of tartar buildup on her teeth? She may just need to be knocked out and have her teeth thoroughly cleaned to get rid of the bad breath. If that isn't the cause of the halitosis, you'll need to consider more serious problems like diabetes, kidney or liver failure. Don't forget to bring this issue to your vet's attention.
I'm so happy that you took responsibility for this little girl when you found her. Congratulations on being a great doggie parent! Since you don't know her entire medical history, I know it makes it frustrating and difficult to figure out her health issues. Try not to fixate on this lump being cancerous. There are too many other things to consider before jumping on that particular bandwagon. So far, I think your vet has provided reasonable treatment. Just keep after him if the antibiotics don't resolve the problem.