how long does spotting usually last while just starting birth control?

I've been on Blisovi Fe 1.5/30 for about 3 months and have been skipping the placebo pills because I want to cut down on my awful periods. I've been spotting for about 3 weeks, almost a month now. Sometimes it's heavier at night. Is this normal? I called my gyno and she said that it's pretty normal but I wanted to see if anyone else was on this and had the same problem.