I've been taking phentermine for about 2 weeks now and I also take levoxyl .175. It seems like about 2 hours after I take the Phen, I feel overwhelming exhausted. It feels like I can't do anything during this period of time, it lasts for about 2 hours. Sometimes it I get 2 or 3 of these episodes in a day. What is going on? I can't find any info.