What should I do?

Hi there
Despite now having a new job, which is fantastic, I have a rather big problem with my previous employer.
Well, how I got the job was at the start of 2003, in my hometown of Reading. I decided to opt to join Superdrug, over about 5 other offers, as I was impressed with what they had to say. I wasn't dissapointed, but as my A-Levels were about to get underway, I decided I'd like to go to University in Liverpool or Nottingham.
However Reading's Superdrug told me they would like to, and will transfer me to another Superdrug.
Leaving Superdrug in Reading was always going to be a strain after the respect of my fellow employees I had built up. I decided to go to Nottingham, and in September 2004, left the Reading store.
I was instantly thrust into work at Nottingham, and did all I could to help the company, after all, higher positions and wages were, as the manager in Nottingham told me, up for grabs.
Well, one Friday, Michelle asked if I could work, and I worked around my lecture, running across the city to get to Superdrug.
However that day she pleaded me to do a day I couldn't do, because of exams. On the Saturday, she began tormenting me. She said I wasn't up to standard, which was utter rubbish and slagged off my old store to my face.
Then she scheduled me in more days I couldn't do, and threatened to "take it further" if I didn't attend. I didn't, and therefore, the situation spiralled out of control.
She decided not to pay me for any of my sick days, even though I had a valid doctors note.
I left Superdrug furios, and took the situation further myself. Head Office recieved my letter, but Nottingham's area manager seems to be siding with Michelle.
Who should I take this situation to next, and should I make legal procedings, which I dont want to do, as Superdrug in the past have been good to me, but I cant let Michelle win.
Any ideas would be much appriciated.
Craig