you will always feel like that if you try to take your clen right before you workout, including your weight training. imagine trying to do a real heavy bench press after about 200 push ups. clen not only raises your heart rate but pressure too. your heart feels like its working hard before you even start exercising. then you double its load when you start your workout. so fatigue sets in alot faster in you heart and most of the time in the rest of your muscles too.
and ??? maybe i missed it but are you taking 80 mcg all at one time?