Were you married?
Is your name on the birth cert?
Can you not get a solicitor involved?
Does she drive? Is she willing to meet you half way perhaps? There are holidays and weekends - you devote what work time you get off to your son and you will see him more often than you think
It's unlikely you will be able to stop her moving up North BUT if your name is on the cert you do have rights.
You're right, a 2 yr old cannot travel 3 hours there and then go back again the same day - but you can. Move hell and high water to see your son for your son's sake not your own