Your job is taking a toll on you this cant be said rationally, all that is lacking is adjustment on your part. First you need to balance your daily schedule. Kindly take note of the following:
1. Have 6-8 hours of sleep(undisturbed)
2.Add a schedule of exercise/game/swimming/cycling/aerobics
to your schedule, coz you have a sitting job your joints and muscles should be in good shape.
3. keep on changing posture after sometime and do not turn or move at once, do it easily, because sitting in one posture and at once moving from it at times stretches ligaments or you can have a muscular sprain
4. Do some stretching in some intervals by getting up from your seat.
5. have nuts in your diet alomnds/walnut they will provide you extra nutrition
6. have meals on time if possible 3-5 small meals or 2-3 major meals & 2 small meals in a day
7.avoid excessive fried snacks and high calorie diet
8. If you are still loosing weight, then consult a physician to rule out any medical condition.
For any queries please feel free to wish you a speedy recovery and health