Can you contact the paediatrician and remind him he said he would get back to you about melatonin and MRI? Sometimes they do forget. Alternatively, could you ask to see a different paed?
I've been very lucky recently I was going to write an almost identical post yesterday - DD was born very premature (at 27wks) and had quite an easy ride through SCBU, she made good progress to start with so by a year old had been discharged by everyone (physio, consultant, eyes, ears, etc). She has been seeing a physio since December (at 1y 8mo) because her gross motor skills development had 'stalled' at cruising for about 6 months. Physio has been keeping an eye on her, seeing her every 4 weeks or so and then in April decided that she was concerned enough to refer her to the community paeds and orthotic dept as she was worried about CP.
That was in mid-late April. Since then we've had weekly physio at the local CDC. Early May brought the orthotic appt where they agreed to give her neurological insoles, early June brought fitting of those insoles and paed appointment where we got a positive CP diagnosis, and today we had an appt with physio who has promised to refer us to the OT dept and a phonecall from the paed apologising that we hadn't had the letter about the appointment 3 weeks ago, checking we were ok, telling me who she'd referred us to (joint paed/orthopaedic clinic, hip x-ray and Family worker to fill in DLA form) and offering to visit us at home one day to talk to DH about the diagnosis!
I'm amazed because my experience of our PCT until now has been pretty dire, so this has blown me away completely! These are people who get things done! (Sorry, doesn't help you, but just to say that there are some people who are good at saying they will do things but need reminding, and others who actually do them!)