Does obsessive thinking about work cause you to have insomina?

It certainly can. The most common reason these days for insomnia is the failure to "wind down" from the daytime activities and thoughts. In part this is because we have created a world in which artificial light and technology allow us to be busy straight through to bedtime. Unfortunately, our brains are still designed to work in a world where the sun slowly sets and then we go to sleep with not much happening.