Problems meditating

I am having a lot of trouble meditating tonight.
I am too tired I think.
It starts out fine: I close my eyes, feel my diaphram expanding and contracting, watch my breath go up and down. I concentrate on the rising and falling of my breath. After just three breaths my mind is off and I have a hard time wrangling it back to the breath. It was like I was dreaming and in my mind I was trying to remember what it was I was supposed to be doing. My thoughts would confuse me so much, I would be left wondering and totally baffled, like I was about to say a word, but I forgot what the word was, and I was searching through my lexicon to try and find it. Or that the fragment of my concious that had drifted off was trying to follow the rope back to "the mothership" or purpose. I've tried three times and each time it ends in my pretty much asleep and practically dreaming sitting up. I begin to observe my mind like I am supposed to be, but instead of acknowledging and naming the feelings that arise (as I was able to do the first time) my mind subjects me to dream visions and whisks me away and I forget my purpose. Interesting that I am similarly confused occasionally in daily waking life.
I will try to observe my emotions and thoughts tomorrow througout the day as the mundane details of office life try to irritate my psyche.
A lot of my negative feelings come from the fact that I perceive myself to be wasting time with my job and that what I do is virtually meaningless.
It is, of course.