It could be Tietze syndrome. Tietze syndrome is similar to costochondritis, but includes swelling.
Be sure to report it to your doctors in case they want to verify that that's what it is. Tietze syndrome is not a serious thing, although it can be quite painful.
And stop poking at it.
That will just irritate it and make it worse.
Ginny - 57 year old female
Dx with USpA in March 2013; changed to AS in July 2015
Iritis and Scleritis
unicompartmental knee replacement June 2014
MTX, Humira, Cyclobenzaprine, plus Indomethacin ER as needed
Supplements: Folic Acid, Vitamin A, Vitamin D, Calcium, Fish Oil, Melatonin, Culturelle probiotic