Sounds a lot like costochondritis. But with irregular menses, I hope you are getting your thyroid levels, FSH, LH, prolactin (if discharge occuring), and anything else a doctor thinks should be checked. Thyroid problems or even a pituitary tumor (they say one in five has one) can cause menstrual irregularities.
Welcome to the MedHelp forum!
Generally breast pain that comes and goes and disappears in between is due to fibroadenosis. This is a benign condition and often there is no lump associated with it. It generally responds to drugs like Danazol. Pain felt primarily under left breast is often due to acidity and gastric reflux. It can also be due to costochondritis. Since there is also delayed periods chances of PCOS is there. Both these conditions can coexist. I think you should discuss these possibilities with your gynecologist. It is difficult to comment beyond this without examining. A comprehensive investigation is required keeping all the points in mind.
Hope this helps. Please let me know if there is any thing else and do keep me posted. Take care!