How do I control when to cum (30M)

I've (30M) been with my gf (28F) for 3 years now and we have sex pretty much every time she's able to visit me for the week.

The first time we did it was my first time, so I wasn't surprised that I came in under a minute. But now, even after 3 years of sex, I find that a majority of the time we have sex, I'm still cumming way too fast; maybe not a under minute but definitely under 2-3. And there are some days when I can't cum at all, which is usually when we do it without a long enough break in between.

I've read some comments saying I could actually control when I do cum, and the one I've tried so far is thinking about something not sex-related during if I feel like I'm about to cum. I mean, it definitely worked that I didn't cum but my penis went flaccid almost instantly. I tried focusing back on the moment to get it up but I got so frustrated that I couldn't. I tried using the strategy a few more times after thinking I shifted my thoughts too early, but still yielded the same result.

Another tip I've seen is having her grab the head before I feel like I'm gonna cum to try to deflate it but it just made me cum even faster with her hand on it.

I'm leaning towards that I just don't know how to properly control when I can/can't ejaculate. I wanna be able to last long enough that she cums from PIV since I always end up finishing her with my fingers or oral. I know she definitely can cum from PIV because one time I ended up not being able to cum after maybe 5 minutes she had reached climax but I couldn't. Could this also be a sign that I have premature ejaculation issues?