problems with erection after pumping

[stanly]

Hi everybody!
I'm quite new to pumping, but although an often visitor of this forum. So a few months ago I bought a vet serynge (150 ml),that's all I could find at an affordable price cut the end of serynge and started pump. My dick size is 13 cm. That was great till I realised that I have problems with hardening on. So I let the serynge apart for some 2 weeks and everything came to normal. Then again I started pumping and the same problem I got.
So tell me please is it normal to get these problems, I don't think so.