I'd have thought 100 psi should be well in the ballpark for that kind of weight, perhaps even a bit on he high side. I'd suggest you might have a fork problem there. Time for a service, see what that reveals, unless you can love without the lockout until re service is due.
Long term you got 2 choices - spunk out on more upmarket forks, which might not be justified on a cheaper bike (I don't know what bike you have). Alternatively, have those forks serviced and set up by a pro. I got a set of Tora coils I had professionally sprung and Valved to suit my weight, 112kg. It cost £200 but te performance improvement is stunning. The coils are are heavier and pronento be noisier but give a better progression/rising spring rate than even the best air forks. Not being too worried about weight and being a heffalump myself I went for them.
Sadly, as time goes by I'm going to be forced onto air forks as fewher manufacturers do a decent coil unit.
Anyway, enough of my rambling. A pro rebuild and custome valve job would cure our problem if you can stomach the expense. They're supposed to be serviced every 50 to 100 riding hours, so pure probably not far off needing the service anyway.