Armpits only smell when I go outside?

Name: 
Ana
More information: 
I don't sweat much. However, if I go outside when it is mildly hot out, my armpits smell terrible. On the contrary, if I'm at the gym and sweating buckets, there is no smell. Also, if I'd go outside and run (sweat) in winter, no smell. Please help as I've tried so much for this.