You'll need to wait for biopsy results, but "Gynaecomastia is found among people who take Doxazosin mesylate, especially for people who are 60+ old also take medication Casodex, and have Prostate cancer."
8,192 people reported to have side effects when taking Doxazosin mesylate. Among them, 9 people (0.11%) have Gynaecomastia
"Stop taking it" may not be the answer; man boobs may be a lesser problem than the one you started with, and (in most cases) the effect isn't reversible.
But - depending how long you've been on the medication, your doctor may be able to reassure you that they are unlikely to get any bigger.
-- Andrew --
"I intend to live forever, or die trying" - Groucho Marx