Did you burp him properly after feeding?
Dont shake the milk bottle, stir with a teaspoon.
Use boiled water some bb cannot tahan filtered water
A good design bottle like mum or avent with anti colic will help.
Personally I dun think accidently pulling the cord out will caused bb to get colic.
Most baby starts colic season around 3 - 6 months, my bb oso the same, but not really bad

And the last thing is I duno if this is a proven thing, my CF lady told us to put bb on this thing
"Probiotix Biolife Reuteri drops" on the 2nd week, she swears this thing works to reduce bb colic in later stage. Its quite difficult to find and cost around RM110/small bottle. I found mine from a pharmacy at pudu plaza. Luckily you only need to give 1 bottle to baby.

If you want picture of the probiotix pm me

hope this help your problem, if too much headache then you should just go see your paed