I am 20 years old and have mid-arch pain on my instep.  I have very flat feet and this only started recently with my new custom orthotics. Should I go back and get some new ones made?  

Depending on your flat foot flexibility, you may not need orthotics at all and often custom orthotics can increase the pain in a rigid flat foot deformity. You might try no orthotics at all with some good calf stretches to see if this lessens your instep pain.