Hair loss

For the past month or so, I've been losing a lot of my hair. Not balding, per se, but my hairbrush gets filled up pretty quickly. I thought it might be because I stopped taking those prenatal vitamins, but I figured it would slow down after a couple of weeks if it was that. I'd say this has been going on since the beginning of May. I did some Googling and found that hair loss is common 3–4 months after a major surgery. That fits my timeframe. But it didn't say how long it will last :(