New Rear Wheel goes out of true Couple of months back, I installed a new rear wheel for my road bike. Its a wieman LP18. 

Since then I had to get it trued at-least three times. Is this normal for new wheel?
It's normal for a new wheel that was under-tensioned, unevenly tensioned, inadequately stress-relieved or whose spokes are twisted.

Either that or it's being abused - ie. if you're really throwing it around, or are carrying heavy loads on the 24-hole version.

The repeated re-truing may end up with a decent wheel, since you're just performing the stress-relieving step while riding instead of in the workshop. It may equally damage the wheel before you get there, and you really shouldn't have to pay to fix a bad build.