At the moment it feels like everything is going wrong: I've lost power, motivation, and even lost some weight and strength. I feel tired most of the time and I'm getting a bit worried. Has anyone else ever felt like this? What can I do?

Here is some information about me; I'm 17, 6'3, currently just under 13 stone, I am (usually) fit and strong. I was 13 and 1/2 stone at the start of the summer (around 190lbs). Then i went on mountain climbing trip for two weeks and lost half a stone but I was not that bothered because it was some fat as well as muscle. I haven't tested my bodyfat for ages but I would estimate I am around 12% at the moment. I thought that this endurance and lung size increase would help my fitness even if i'd lost a little strength but since then i have a lost another few kgs in the last two weeks; and have found it really hard to force myself to train properly. I row and was aiming to do a few 30-40 or even 60min seesions on the rowing machine that I have. But I just don't have the motivation. I was also doing power training and max HR stuff a few days ago and I just had no energy after the first couple of intervals. I have been doing some summer work as well on random days through the week which really screws up my plans. I am now just working on the weekends so I have a good chance to do some decent training over the next few weeks. I bumped into my coach yesterday and he said not to worry about max effort power pieces so much as the body cannot continue this all year round with continuing success and told me just to concentrate on long endurance work. I have started taking 500mg of vit.C a day as well as a good multivitamin.

Have you got any advice to get me back on track?