Maybe your calling isn't supposed to make you happy. I heard a very interesting quote regarding ministry one time that basically said that while some find happiness in serving, some might be called to come, to work, to question, and to die; happiness and being content might well be a luxury and not a promise or requirement for filling a call. Seems kind of odd, but it makes sense. Does that color the idea of call in your mind? You might be feeling a lead to do something completely foreign to your nature (like leaving your tax collecting booth and good living to follow a mystical carpenter), something crazy uncomfortable, and you might be thinking that there is NO WAY God would call me to do that...what if God isn't so concerned with your comfort as He is accomplishing His agenda? How does that sit?