Breaking the coffee habit

I never realized how much coffee was part of my routine until I stopped drinking it last week. I've been sleepy and sluggish since then. But I must break this habit. I want to be able to go without it. I've been drinking coffee every day since I was 14. I've tried going without it before, but by the second day of not drinking it I would get massive headaches. I've been cutting back for the last few months and finally last week I stopped drinking it altogether. I've been drinking tea to alleviate the headaches. I think I've passed the point of the worst headaches, but I still have difficulty staying alert throughout the day.