My dachsie went to a new groomer 2 days ago, and since then she has developed a bunch of (small- bb sized) bumps on her back. There is one bump larger than the other just above her left armpit. The bumps are red, not crusty and don't have any discharge. She doesn't seem to be scratching at them. I tried giving her baby benadryl (she has previously taken it to soothe bug bites). We live in a northern climate, and insect bites are not a possibility. She's an indoor dog and has never had fleas- checked her very carefully this morning.

Could have been bitten by fleas at the groomers. Give them a call and let them know. Maybe they have an answer

I think the groomer might've used a chemical that your dog may be allergic to. The same happened with my dog and she's been itching and losing hair. You should really ask the groomer what He/she used on your dog and they should have the answer to this problem. My mom usually treats it by cutting off hair from the irritated area and cleaning it daily with peroxide. If not, take her to the vet.