Samsung Galaxy S4 Active — My Samsung wont work on the usb on-the-go. I wanted it so i can use a portable charger,

Ive already put on the designer mode, and then the, euh, usb-thing (i am a complete nitwit, sorry), but i cannot connect it to my external loader. I hope someone can help me, for i dont know what to do anymore. By the way, i have checked if i had usb OTG, and yes. But it doesn'work.
Thanks in advance, although i doubt it that anyone can help me. I'm about to give it up.
Monique