Can’t keep it up post-orgasm anymore

29 M here. When me and my partner if 10 months started dating, I was able to stay erect even after orgasming. That’s been a general trait of mine for a while.

Lately however, I haven’t been able to keep it up, and that worries me because I generally climax really quickly. I had been depending on this ability to get her off multiple times, but now my ability to get her off even once is limited. She deserves better.

What’s happening to me? Is there something I can do differently to get that strange stamina back?