Recently started birth control

Hi guys! So I recently started birth control a couple weeks ago. I already had my period this month so I started it after it ended like my doctor said and today when I got out of the lake, I saw blood in my bathing suit bottoms. I thought it was because of all the new hormones and me training for the marines. But I just noticed that I’m not bleeding anymore. What does this mean? I’m 17 btw