I have swollen, tender lymph nodes on the left side of my neck and just above my clavical. no other symptoms. could it be cancer?

Very unlikely: Tender nodes that are not obviously abnormal and aren't growing rapidly or matted to the surrounding tissue are almost never cancer, especially at your age. I'd watch them. If your current acne medicine isn't strong enough to manage it, this itself may be the cause. Best wishes.

Cancer?: Tender lymph nodes are usually due to infection. See your doctor. They would likely put you on antibiotics and see you again in a couple weeks. If nodes still enlarged they may suggest an FNA (fine needle aspiration) where a small needle is used to collect cells that are submitted to a pathologist for an examination.

Unlikely: Enlarged lymph nodes can be due to cancer but in that case they typically are painless. Infection related enlargement of nodes is often tender. if the nodes do not settle down in 2-3 weeks, you should get checked by your primary care doctor.