Spotting on Active Pills

This is my third brand of birth control pills I've tried since August, because the last two failed to regulate my periods. I ended up getting them multiple times a month instead. I've just started this new pill a few weeks ago, but I've already had spotting twice. The first time it happened, I went back to the doctor and they told me not to worry about it and to keep taking the pill. But since it started again, should I go back?