STrange Behaviour of the plane

Hi Guys!

I have a little problem with the NGX! I tried to fly on line on IVAo and i used IVAP and the weather engine of IVAP. Soon after take off and flap retraction the plane started to bump up and down and the speed started to increase and decrease like there is a really strong turbolence. It is so strong that te autopilot disconenct and the plane start to roll till stalling. I gave the fault to the weather engne of IVAo so i disbaled it and started the flight again using AS2012 but i had the same problem after flap retraction i started to have the plane nose moving up and down. The AS2012 weather engine is set on DWC. Should i select smooth cloud transiction? Or the problem is another? I read the DWC can give problems of S-Turn but my plane dont make S-turns just start to move the nose up and down like crazy..

Thanks