Changing a sleep cycle, especially drastically, takes time for you body to adjust to. It's pretty self induced jetlag and you're trying to yank your entire circadian rhythm to another setup. According to webmd, and answers on Quora, jetlag can last 4-5 days, but varies by person and time adjustment. (Three days was almost there!)
Your circadian rhythm, sleep playing a large part, entails a lot of aspects, all which need to adjust to a different sleep schedule. Consider how your eating, exercise, and the rest of your daily rhythm comes into play.
Lastly, consider using other sleep hacks to help adjust. Searching for adjusting to jetlag will provide plenty of tips. Here's a really long answer I wrote on Cognitive Sciences Stack Exchange on sleep hacks.
Best of luck!