Well I'm a retired Master Watchmaker so........
First, all mechanical devices need a break-in period, but your watch should be broken in.
Watches are adjusted at the factory to keep precise time. The trouble starts when a real live person puts it on. A watch will gain or lose depending on the person wearing it. A very active wearer will get one standard of accuracy, and a less active wearer will get a totally different accuracy, for instance.
The adjustment made at the factory is a "best guess".
I can adjust a fine watch to keep almost perfect time on MY wrist, but on your's it will likely gain or lose.
In your case, just take the watch to a factory authorized dealer, and have it adjusted. It may take a trip or two, but it will keep a better standard. Having to have a new high-end
watch adjusted for maximum accuracy is standard procedure. Most people either don't know about it, or just don't bother.
You do. See your dealer.
Why does a watch keep a different accuracy when worn in different manners? Because the case, and therefore the movement is in a different position. Put a watch movement in a different position, and it will run differently.
As to "Body Magnetism", this is one of the oldest "urban myths" about watches there is.
Here's an explanation I posted on another forum some time ago:
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Ok, here's some hard talk from a retired Master watchmaker, NO DISRESPECT INTENDED: Just the facts from a pro.............
Years ago, the complaint was "My chemistry or Magnetism or electricity stops my mechanical watch" Now days it affects electronic movements, but sometimes NOT mechanicals.
Chemistry can have no effect on a watch that's sealed in a water resistant case. If chemistry was responsible, the movement would be rusted or corroded, and the case would be damaged.
I have seen many watches exposed to harmful chemicals, and in every instance, the watch case was damaged, and the movement was corroded if the chemical penetrated the case.
There is no chemical exuded by the human body that can stop a watch, without corroding the movement. If it can't get inside a sealed case, it can't affect the watch. Period.
If you had enough "Magnetism" or "electricity" in your body to affect a mechanical or quartz watch movement, (both of which are ANTI-magnetic by the way) you could stick a light bulb in your mouth and light up the room...., LITERALLY.
There is no function of the human body that can drain a power cell or affect a watch movement. Otherwise you would have problems with flashlights, cell phones, and car batteries.
There are strong magnetic fields that can affect watch movements, mechanical and electronic. However the human body can't generate such a field unless you're an "X" Man. Watches exposed to that strength field will either stop functioning instantly , or will be wildly inaccurate.
Watchmaker's are constantly being told by people that there's "something" about their body that stops watches or causes inaccuracy.
We hear this constantly, we try to tell people this just isn't possible, but the legend persists.
The reason some people have problems keeping a watch running is just a matter of bad Karma, The Fates, or just pure "bad luck". I have had these people as customers, and most believed in the "electricity, magnetism, or chemistry" explanations. I long ago gave up trying to explain sealed cases, anti-magnetic movements, and physics.
Some of these people are sure they can "Kill" a watch, but never consider the fact they have no problem with a hearing aid, cell phone, beeper, or other device.
We learned long ago to just evade the question, because you can't win these.
Why do some people have watches that just quit or won't run properly? Body electricity? Body Magnetism? Body chemistry?
Why not that the "Watch Gods" just don't like you. That makes as much sense.