Hi, I have an Omega red gold Constellation watch. I noticed that it was gaining time in the first year and the same in the second year. After two years, and constantly changing the time and putting it right, I took it to the jeweller where I had first bought it and said how disappointed I was. I said I would have thought an Omega would work to perfection, after all they advertise in world wide sporting events. The guy in the shop said it was out of guarantee but he would see what he could do. He advised me that the watches are calibrated to normal wrist movement but some people need the calibration altering to suit their individual needs.
It was sent back to Omega (Swatch/Rolex - they're all one now) and they calibrated it free of charge and I never looked back for four years, it didn't lose nor did it gain. Then because I was not wearing it regularly a couple of people advised me to buy a watch turner otherwise the internal parts might corrode.
Great!!! Now the watch turner has a movement which is different to my wrist so consequently because my Omega was 'slowed down', whilst it's on the watch turner it moves faster than my wrist and so 'gains' time. I can't win but I adjust it when I wear it and it works perfectly again.
It's a simple matter of calibrating the watch for you. I am surprised that this hasn't been done for you as the guy in the jeweller where i bought it, knew straight away what was wrong and had it rectified.
Good luck