hehe... those are stretch marks. They were probably there before, you just didn't notice them. The purplish veiny look will fade out in time, but a stretch mark is basically a scar caused by the skin expanding faster than it was designed too (i.e. it happens when you gain a lot of weight or grow really fast in a short period of time). They will fade into something silvery and less noticable.

Since these marks seem to be "fresh" as they are still purple and veiny-looking, try using retinol a or cocoa butter on them. These treatments help with fresh marks, but once they fade out there is nothing really you can do for them... short of surgery/removing stretched out skin.