What is happening with my erection (33M)

So I’d like some advice about what the heck is going on with me. I am 33M.

As of the last year, I’ve been having an issue with getting a hard on especially when I most need it.

I can get a hard on throughout the day when I am stimulated visually or when I think about women. Sometimes I also still get morning wood, but not daily like it used to be.

This tells me that physically I am capable of getting a hard on and that there is nothing wrong with my veins and blood flow.

However, when I am masturbating, whether I do it myself or my girl is helping, I can only ever achieve at best a semi hard erection. Sustaining it is also an issue. As soon as I start to shift around, I get softer.

I can achieve almost 90% erection, but this is only just before I am about to cum. A few seconds before.

Also, its difficult for me to get an erection when I am sitting or standing. Best is when I am laying down in bed.

I’ve been watching porn daily and masturbating once a day for awhile now.

I am thinking about laying off the porn for a whole month April and see if things improve.

This is really starting to worry me. Any advice is appreciated.

I am a bit overweight, but I’ve been the same weight for the past two years already.

What could it be?