My understanding is that it wouldn't matter, necessarily, how long you've been taking it. It's a combination of how it effects your hormones, what your hormones are already like, your genetics/pre-dispositions, the length of time you've been taking it, and how your hormones are changing (especially considering you're at peak baby age). I am not a doctor, so I'm just speculating. The Ortho could have been making you lose hair when you were younger too, it was just less hair so you didn't notice, but again I don't think that even matters. A change in your hormones could be causing hormone-related hair loss, and the Ortho could be what's aggravating it.
You have to look at it this way: What could be causing hair loss in your life?
The birth control that you're taking that's known to cause hair loss
Stress and anxiety (perhaps even caused by your hair loss). Not all stress is "felt", and some people thrive on eustress. You're an adult, and being an adult is stressful in like 10,000 different ways.
The products that you put in your hair
Aging
Weight loss
You have plenty of reasons to be losing hair, theoretically. If it's really "way more than 100 hairs per a day" then something is obviously amiss. You can't start looking outside causes until you rule out the things you already know could be causing your hair loss.
You've already seen the a doctor, he said you were fine, and he suggested it might be related to your diet (in general, that makes it less likely that one of the physicians in this subreddit is going to respond, because they're just going to say "go see a doctor").
So what's left? It's either one of the factors I listed, a combination of those factors, an obscure deadly disease, or Alopecia.
So what can you do? Try a different birth-control medication, one that isn't notorious for causing hair loss. Stop using hair products besides shampoo and see if that helps. Go to another doctor and get a second opinion. Or go to dietitian, but let's be honest, what could you be eating that's causing all your hair to fall out?
My bet is if you stop taking the birth-control, or switch to a different birth control, your hair will stop falling out (but even then, it could take months for your hormones to readjust). This is probably being caused by a hormonal change, which means you have to readdress any medications you're taking that might be messing with your hormones. And, no surprise, you're taking a medication that's specific purpose is mess with your hormones. You have to start there, or you're never going to be able to figure out what's going on.