Took Ambien (zolpidem) 10mg for 2 year's. My dr changed me to 15mg diazapam. Not working for insomnia. If I already took the Valium 20mg can I take a 10mg ambien (zolpidem)?

NO -- please don't! Please do not take valium and Ambien (zolpidem) at the same time! you could end up overly sedated. Also, valium is not meant to be a sleep medication anyway. Please tell your doctor about this. It sounds like insomnia is a very significant problem for you, and needs further investigation (maybe sleep study?). Both Ambien (zolpidem) ; valium produce tolerance, making long-term use very problematic overall.
You. May. Why did your. Dr stop ambien (zolpidem)? You. Did not tell your. Age . Why did your dr start valium? If you needed something. For. Anxiety. Lorazepam. Would have been better . In my opinion both drugs are in the end are monster but if you had to take one. Take the one. Which helps you with least side effects . I would not take both just to sleep .Valium can give you more problems if you had to stop.