I can't pretend that I know what's going on with your DS, but try not to despair TOO much. Annoying as it is, 14 or so does seem to be the age at which we feel like they are slipping out of our control and we don't know them any more. "Where's the little lad that used to cuddle me and did almost everything I asked?"
My DS is 16.5 - and when he was 14, Id gotten to the point where I had moments of actively disliking him. I hate myself for admitting that, because I never stopped loving him - but "like" was a different matter. Overnight he became rude, argued about everything, stopped doing any homework at all, swore at teachers, told me he hated me continually, emotionally manipulated me...the list is endless. Even getting him up for school was such a hassle I'd start my day in tears. It was a bloody nightmare, quite honestly - and I, of course, blamed myself for everything.
But he got over it simply by growing up a bit and he is a different person today.
Example: One of his GCSEs is IT. Soon after starting the course he decided he hated it, hated the teacher and wasn't going to bother doing any work for it. So he didn't. None. Nothing I, or his IT teacher could say made the slightest bit of difference - no punishment worked, no threat. "It's my life, I'll do what I want". This went on for 18 months. I, and his teacher, assumed he'd get a U grade.
About 6 weeks ago, his IT teacher took the whole class aside one by one to talk to them about what they could do to up their grades in preparation for the final exams. To my DS he said, "Well, we're looking at a U currently. If you do some work now, we might get that up to an E, or possibly a D".
"OK" says my DS. He went in every day after school for 2 weeks and worked solidly with the IT teacher. He's now expected to get an A. IT teacher bought him a bag of Haribo (:)) and has used him as an example of what can be achieved.
I'm not just trying to stealth boast not too much, but just trying to reassure you that teenagers can, and often do, leave us despairing. But more often than not, it comes right in the end. They just need to grow up a bit.
My DS today is unrecognisable from the person he was just two years ago. So hang in there - loving, consistent parenting does make all the difference, it just might take a while to see the results. But you will :)