My 6week old is having v smelly runny poos v smelly gas and has been quite unsettled the last few days, not sleeping well? Could this be his formula?

Possibly. If you have been using the same formula since baby was born and are mixing it the same way, it's unlikely it's his formula. However, if something has changed, from formula type to the water you use to whether you use powder vs ready-to-feed, it could affect him. As likely, though, is that he may have a little stomach bug . If vomits, use a feeding of pedialyte, but if persists, call your peddoc!