I'm sorry to hear of your loss. I, too, was alone after my mother died and even though I was a grown woman in my 40's, it was very difficult being alone at that time.
One of the things that helped me was joining a grief support group at the local hospice. Most hospices run them every month or so, and you don't necessarily have to have used the hospice to join the grief support group.
Also, one other thing...it is so very hard at first to remember the happy moments, especially when all you can picture is how your loved one looked the last few weeks of his/her life. If you have some, you may want to pull out pictures from before your Dad got sick...they may make you cry, but they also may help you remember the happy times.
And, I truly believe that you are not really alone...your Dad is always going to be with you in your thoughts and your memories.