Dark underarms and inner thighs -- is the darkness also present on your neck - as this can be acanthosis nigricans. Boils on inner thigh can be bacterial or fungal infection - will need to examine to comment properly. Stretch marks treatment will depend on if they are new and red- for which creams can e currently used .. or old and white- for which laser treatment will be more effective. Unfortunately without proper examination of the lesions and the needed test reports i am limited with my capability to assist further. Hope this was helpful.