Flatwhite - your job does sound extremely demanding and stressful! I know it's hard but I think it would be a good idea to reduce your hours if at all possible. I know you say there's nothing you can do about it, but is there anyone you can talk to about it to at least broach the subject? I don't think it would be unreasonable to ask for less than 100 hours (which I'm sure you're not contracted to do?!!!) You probably need to be a bit less willing - the more you take on, the more they will keep on expecting of you. I understand it's difficult because keeping a stable job is all the more important at the moment when ttc isn't it?! BUT they aren't going to fire you for not working at a million miles per hour - they have to have good reason and show that they have given you appropriate support before it comes to anything like that. For me, it's less about the actual hours and more about meeting deadlines and the quality/nature of the work which needs to be bang on. It can be very intense. What I've been doing is making use of more senior people in my team, asking for support/guidance rather than taking accountability for everything. After all, they are getting paid more! That said, I'm not sure how senior you are so it may be more difficult for you. In terms of relaxing - long baths, trying to switch off when you arrive home (e.g. no work email rule), massages off your partner, have fun (go out for meals, to the cinema, for walks), exercise, eat right (sugar and yoyo eating, which is common when your hours are long, will only add to the feeling of stress as it will mess with your blood sugar levels). Take care of yourself and remember: on your death bed, are you going to look back with fond memories of your career or your loved ones? In the grand scheme of things, money and work isn't important in life; the people in it are. Sorry for the long ramble!!
Cinder - don't let it get you down! As long as you are eating healthily you will be absolutely fine. People of all shapes, sizes, ages etc etc have babies every day. Listen to your GP and keep at it 
Thanks for the tips ladies! Looks like I can 'O' guilt free now
...when dtd isn't too much of a chore that is!
On another note - on day 23 now and still no positive OPK :( I think my boobs are getting a bit sore though?! I hope it's round the corner. One thing that confuses me is that i seem to have had ovulation CM for about a week now?! Confused.