Adipex Questions, Help? Anyone?

So, hello!
First, let me say, I probably did a HUGE mistake by just taking the pill before doing a lot of research.
I took it two and a half hours ago, and my whole house is cleaned, I've done my 18-month calendar update, and I'm a little freaked out.
It's not that I'm that lazy, just.. It's 10:30 in the morning, and I am NOT a morning person.
I've steadily gained weight despite diet and exercise for about 5 years. (I'm 23, so basically I started gaining weight when I was 18, went to college, stopped relying on parents to feed me. I know, I know, shame on me.)
I bloomed from my fluctuating 140~160 to a robust 222.4 lbs as of yesterday at the office.
So, the doc off handedly wrote me an RX for phentermine 37.5 mg, once daily.
I work in a pharmacy, have seen a lot of people on it, but never really contemplated it or how I'd react to it.
Now, I don't care how well it works or doesn't, I'll only take a half tablet tomorrow.
(Wow, sorry, I'm realizing I have not done anything yet but tell you my life story - Sorry!)
My question is: Does anyone have any suggestions with this drug?
I don't eat bad per se, but I don't always eat healthy, either.
I live alone, so I eat fast food more often than I should, and rarely cook.
I've heard some horror stories of eating fast food while on certain diet drugs that just cause a mess in the bathroom, that's my real worry, because as much as I'd love to eat 100% healthy it's just not realistic, and I have work with one bathroom, and a lot of co-workers, and I'm not that mean.
And, any other advice would be great.
Like how long it'll take this to wear off, because I feel like I'm about to go a little crazy.

Thanks!
(P.S. If you read all that: I'm sorry. I swear, I'm usually not that blabber-ish.)