Have you saved anything new on this formatted USB flash drive since then?
Nowadays, the formatting process, especially the quick formatting process, often will not erase everything on the drive immediately. As long as the stored data is not overwritten by anything else, it will be reserved there forever. Therefore, you’ve better take care not to write anything new on this drive.
And then, in order to rescue your data back as soon as possible, you need a formatted USB flash drive data recovery tool like 4Card Recovery, Recuva and iCare Data Recovery Free, etc.
No matter which one you choose to use, you’d better act carefully all the time.
Note: Always be careful about your important data and never format a USB drive or memory card without a data backup in the future.