Have had what appears to be a stomach virus 3 times in a year. is there any possible reason why i might be more susceptible than others?

Needs assessment : Unlikely if you are making a full recovery in between that any immune disorder. May possibly be something to do with source of infection (eg rural property or food hygiene issue). Also may not be stomach infection but some ongoing bowel condition. A GP appointment might help sort this all out

Unlikely immune: As previously said, this assumes that you have made a recovery to normal bowel function between episodes. 3 x in a year is a bit unlucky but not so many that I would automatically start considering immune issues etc. Do you have children or exposure to children/animals (very common for parents to get these kinds of illnesses frequently)? Other considerations are your work or daily activities.

Improve the Hygiene: We often touch our face without being consciously aware of it. Germs need to get access to our mouth to cause gastroenteritis (stomach viruses), so if we can try NOT to touch our face constantly, this should reduce the risk. Frequent hand hygiene is also advisable - particularly after handshakes, using the bathroom etc. There's a technique to avoid touching dirty door nobs- use a paper towel.