2007 Ford Ranger catalyst converter

I purchased the truck brand new and has been running fine until one morning about a week ago. i started the truck and began driving to the corner store about 1/4 mile away. as i approached the end of the block, i noticed the engine idled roughly and then struggled when i accelerated. i also notice some discolored exhaust when i accelerated. i think its the catalyst converter but i cant figure out the underlying cause. this problem began quite suddenly. i have been making very short trips regularly for the past 7 months. by short trip i mean start the truck, drive 5 mins, turn off the truck for 8 hrs, start the truck, drive 5 mins, truck sits for about 10-12 hrs. this process repeats five days a week. can you please help the mechanically clueless??