I have never done Clenbuterol, nor have I really even researched it, but I'm not sure Clen would be a good choice for you (for right now). From what I hear, you really need to research it well before using it (pretty sure it has some hefty sides), and if you're friend gave it to you, I'm not sure that you researched it adequately. There are plenty of people here that have used Clen (and several write-ups and research articles) on this site in the weight loss section for you to read through though. I could be completely wrong about Clen (or your level of research), but I always prefer to err on the safe side. Also, have you had a body fat measurement done. Your weight could include a large percentage of lean body mass, in which case losing weight might be very difficult, especially with lifting weights 3 days a week. It sounds like you might be at a maintenace level. I gotta go to work right now, I'll check back later. Hopefully I helped, but I'm still learning as well, so I could also be wrong. Hopefully someone responds soon, and please research clenbuterol before taking it. Take it easy.
--Brian