Thanks for writing!
If your tests are negative, you are not pregnant.
Travel in general, not just jetlag, can affect a woman's cycle. It is not uncommon. A combination of fatigue, time difference and the diet and lifestyle change that travel brings (even travel stress, although a traveller may not subconsciously feel it) can all collude to change the cycle. It may take a couple of weeks to sort out, or if returning, may take a couple weeks more. It's usually not something to be concerned about - our cycle is very sensitive to change.