Your assessment findings indicates that pain is most probably due to the pes planus. If you have doubt about the plantar fasciitis, please check the tenderness on heel especially at the plantar spur site.i.e. attachment of plantar fascia at heel. Please, remember any painful condition of foot gives rise to pain in the leg. However, the differential diagnosis of leg may be :
Leg Pain:
Osteitis or other infections
Bone tumour
Stress Tibia fracture
Brodie 's abscess
Anterior Comartment syndrome
Shin Splints
PID and spinal Stenosis
Vascular insufficiency
Thrombopholibitis
Paget's disease
Ruptures plantaris tendon
Painful conditions of foot
Syphilis
Foot Pain:
Plantar Fasciitis
Flat Foot
Plantar Neuroma
Anterior Metatarsalgia
Kohler's disease
Cuneiform exostosis
Tight shoes and stockings
March fracture
Freiberg's disease
Pes cavus
Verruca Pedis
Bunion
Hallux valgus and regidis
Osteoarthritis
Rheumatoid arthritis
Gout
Tarsal tunnel syndrome
Plantar Neuroma
However, if the problem is pes planus, use foot insole, strengthening exercise for foot intrinsic muscles and stretching exercises for tight muscles around lower leg especially calf muscles.