It's probably from the suction on the clit - just irritation. Do you use lube with it?
I wouldn't worry about an STI at all, since it happened just after using your toy, and the symptoms are just around the clitoris.
Give it a few days, don't use the suction toy, and see what happens.
If you don't use a lube with the toys, especially the suction ones, get one that is for sensitive skin, as it won't have a lot of chemicals and stuff you don't need. There are several good ones available. :)
I always use a condom during sex