I saw my doctor last year for a swollen armpit. She advised that it was just a fat tab...But I feel like something is there...?

Axillary Mass. The armpit, or axilla, can be a difficult area to examine. Common causes of swelling include enlarged lymph nodes, fatty tumors (lipomas), accessory breast tissue, etc. If you perceive that a lump is present & your dr. Cannot feel anything, a simple ultrasound may reassure both you and your dr.
Get removed. If it worries you get removed. This way you can find out absolutely. A dermatologist or plastic surgeon could remove it for you.