Hello and Welcome to YT!!!
I use Frontline Plus as it helps with the mosquitos we are over loaded with here in VA. I've never seen a flea on my babies and Barley gets a bath every week.
As for the bump...I've had two experiences with these. The first was my toy poodle. She had a reaction as a puppy, but has never had another one since. The second was Barley (Yorkie) I got him from a rescue group so I had no idea what the bump on his neck was. I took him to my vet and they ran tests on it and $150 later I was told they didn't know what caused it for sure but they suspected shots, and I knew it was not cancer. Within two weeks it was gone, but he was on antibiotics for the kennel cough he came to me with. Hope that helps you some.
I'm off to check out your photos too
)