Hello and welcome to the forum. Thank you for the question and we are sorry you are having this concern! That the issue of breast tenderness comes and goes, the breast heaviness and sensitivity as well with your cycle indicates that this is hormonal in nature. That you stopped birth control means your hormones are fluctuating and readjusting. Many women see an increase in these issues during that. Whenever we have a lump that we find during a self breast check, we should try to follow up with a doctor. I understand this may be a little hard but I would think about what options you have. An ob/gyn which would be less full as they do not treat covid, an urgent care, a telehealth evaluation to determine if you need to be seen, even just advice from a doctor on call at your primary care doctor's office.
What is most likely is that this is a fibroadenoma. https://www.mayoclinic.org/diseases-conditions/fibroadenoma/symptoms-causes/syc-20352752 Fibroadenomas are solid, noncancerous breast lumps that occur most often in women between the ages of 15 and 35. A fibroadenoma might feel firm, smooth, rubbery or hard and has a well-defined shape. Usually painless, it might feel like a marble in your breast, moving easily under your skin when examined.
Please let me know what you think of this information and we will discuss further.