Just to follow up on what Jim said ... what kind of pump are you using? ... Yes the amount of vacuum makes a difference.
Since the pump is your last resort ... build yourself one like in the image = about $37 at Amazon (links below)
Typical cheap but effective pump ($14)
ABN Vacuum Pump ($22.50) (combine the two pieces)
Next ... get a better ring(s)
The "sleeve" Jim mentioned ...
Once you find a ring that fits and holds your pumped erection (should last about 30 min.) ... try several different methods, like folding the ears of the ring up into the pump tube and pump. Have your wife participate ... let her pump you up sometimes.
Thanks for sharing!