Student finance and the OU

I started a psychology degree back in October with the OU I was granted a tuition fee loan only even tho I am studying 120 credits which is annoying my choice to study through the OU was based purely on my 20 year history with anxiety and depression I have recently been made aware that because of this reason I would possibly be entitled to the maintenance loan part too so my question is am I able to apply for this mid year and if so how do I go about this? I have a copy of my medical records would this be sufficient to send them it does state on there the length of time that I have been suffering with this and that it makes me unable to leave the house for sometimes weeks at a time? I am not financially in a position to pay the £60 fee the doctor is requesting for a letter of confirmation. Thank you for any help or advice given