Being in treatment, having to take time away from work, or school/college/university, and not being able to see people can make you feel isolated. Even with people around you, feeling different from your friends and family can make you feel lonely.
You may find it helpful to talk to the people around you about how you are feeling. You may also find it helpful to talk to other young people in a similar situation - this isn't always easy, but there are ways to do this. You will find links below for some social networking sites which you can use.