Got it, thanks!

Only because it implies frustration etc, Uly?

No, emotionally it's pretty neutral. The thing is that the preposition FOR is used to express how long something happened, not during which time. If you wanted to express frustration, you would use the perfect (with the corresponding intonation): This has happened THREE TIMES over the past six months!

I meant you used Perfect because the person was supposed to be frustrated or in anger? Or is it becase of smth else?

Aha, no – the reason I used the perfect is that when you talk about something that started in the past and is still happening in the present, the perfect is the best way to go.