Definitely what Kath said - movocol The daybbefore and then twice daily for the initial.3 days... as soon as your stools start to get bery soft stop as you may get a boit of runs too so do not want.to irritate tummy.
And movicol works brilliantly
Also bananas - have heaps on hand as they are good for both constupation and runs so helps to have them on hand. While contupated oranges are.also really good as they help make you regular.
Just do not overdo it with fibre past initial few days so you avoid my pitfall of overirritating the gut...
Jel.