"Never able to get an appointment or prescriptions"

I have a mental health condition and my repeat prescription is never ready on time and always seems like a hassle trying to get the medication I require. I phone to make an appointment, turn up thinking I'm seeing a gp, discover I've been booked in with a nurse, who is then unable to sort a prescription or sick note out there and then. Despite being off work for several weeks now and a deterioration in my condition, there has been no support or advice given by this surgery. I try to make appointments to see a gp to be told there aren't any and they will extend my sicknote. I don't want an extension. I want to get the treatment I need to get better and back to work.