I am wondering if this breast lump could be cancer? which doctor should i call?

Your regular doctor: You should see your primary care provider as soon as you can. They can then coordinate testing and referrals as appropriate.

Your primary doctor: Your initial evaluation should be by your primary doctor either a family doctor, internist, or gynecologist. They will assess you to determine whether further testing is required including mammogram or ultrasound or mri. Alternatively, you can see a general surgeon or a surgeon specializing in breast surgery to see if further testing is necessary and if surgery will be required.