Not sleeping

As a baby Isaac slept through the night right away. I was so excited and felt so blessed that my first child was so easy at night. Little did I know that just because he slept through the night as a baby that did not truly mean a thing. He continued sleeping wonderfully until he turned five. To me I thought that by that time any problem would have already happened boy was I wrong! Isaac now wakes up anywhere from two to five times a night. This is especially hard for me because i have a hard time falling back asleep once I wake up. Does anyone have any advise on how to deal with a child who wakes up many times during the night?