vara upptagen means normal busy. This is a neutral word that to describe no spare time. ha det jobbigt is kind of negative busy. You don't really want to do this but you have to such as the non-sense order from boss. It is like a hard time.

Pinja, yes, it helped! Tack! :)

Hi Polina! Vara upptagen means that you just have a lot to do at the moment while ha det jobbigt is something negative that have happened to you and because of that not been available. Hope this helped! :)