Sometimes a simple hormone fluctuation can induce a minor shed.
If it's been going on for 2 months straight though then I would be more concerned.
Like what's been said already, go get a Ketoconazole shampoo first and foremost. Nizoral is cheap, I prefer Regenepure DR though although it is more pricey. Nizoral will be perfectly sufficient though, you can get it at Costco.
Also, Minoxidil (I'm sure you've heard of Rogaine) is another option that should be explored if the Keto shampoo doesn't mitigate your issues.
Reducing DHT sytemically with Finasteride, or topically with RU58841 will both help nip your issue in the bud as well, you just have to decide which route you would want to go.
Luckily for you, it doesn't sound like you have used any MPB prevention products yet at all, so you have lots of options at your disposal that should help completely relieve you of your issue.
And that's how it is first typically noticed. After years of use all of a sudden you notice a difference, and little did you know that over the past few years 1/3 of your hair was probably falling out and you didn't notice until it got bad enough to see it.
Hair loss is a slow-ish process, and typically you have to lose a significant amount before it becomes blatantly obvious that you are experiencing hair loss.
I didn't notice it myself after years until I ran a cycle with Halo + Drol + Mast included in it for the first time. My hair got absolutely devastated from that combo. But, leading up to that, it was slowly getting worse the entire time, it just wasn't obvious to me until I had lost so much that it was blatantly clear I was experiencing hair loss.
Just for the sake of being thorough, you should go get bloods for a Thyroid panel done as well. My ex has Hashimoto's Thyroiditis (an autoimmune disorder that causes Hypothyroidism) and she sheds hair like a maniac and it's obviously not DHT related. If you are hypo, then that would explain the sudden loss of hair, although I suspect that probably isn't the case in your scenario. Get your Ferritin checked too.