charlie, sorry, have no real diet tips but I think you have, in part, answered your own question. If you are not over eating then it is probably partly the inactivity during driving and the eating of cr@p late at night, and believe me I know how easy that is to do! You may not need any great changes to your regime except to try a little exercise when you can and to cut down on the late night snacks and eat healthily during the day.
Only thing is with the stretch marks, this would indicate that you are gaining weight too quickly and the skin 's elasticity cannot cope with this, again the late night snacks will not help.
Maybe try not eating anything cr@p after 8 or 9 pm to start with, then cut this back to 6 pm only allowing yourself a piece of fruit or slice of toast for supper, something light but something nonetheless so you don't go to bed hungry. Then aim to cut the cr@ out althgether. Also drink plenty of water (by the pint) this helps fill up the stomach and apparently we humans often mistake thirst for hunger hence the overeating.
If you dont have time to exercise properly because of your job, then set yourself little targets ie, take the stairs not the lift, if parking in a carpark, don't go for the space closest to the door, park further away and walk, or if you are nipping to the shops for a pint of milk, walk ,don't take the car. These may sound silly but they all add up and from what you say this is only recent and believe me it is better to nip it in the bud now while you can that try to lose 10 stone five years from now. But you should congratulate yourself for acknowledging this now while you are in a position to do something about it, you go girl!
Good luck
warpig1