Can't orgasm sometimes

Basically, I'm sixteen and I've been masturbation since about 12/13, me and my partner have been together for a while, and I've pleasured her, and for a month she started for me too, but for about a week and a half, I havnt been able to reach a climax while masturbation, and my partner tried today, but I couldn't orgasm and I had to stop, I felt really bad, and she felt like it was her fault because she could pleasure me, yet now I think about when she did it, I'm really turned on, what's wrong with me? I've been under a lot of stress recently too, could this be a lead to my problem? If you know why, please reply, thank you for your help