I had DS 18 months ago and since then weeing is weird. Unless I am absolutely bursting, it take a bit to get started and even then I have to jiggle all around (lean forward, lean left, lean right) to fully empty my bladder.
Birth was a "straight forward" vontouse but with a fucking awful episitomy that cut thru a large blood vessel and left me nearly hemmoraging to death combined with my uterus refusing to contract. Hence the the fear of docs.
It sounds like you had an awful experience, but please don't let that stop you visiting the docs when you need to. I'm afraid I have no idea what the issue might be, but as your DS is 18mo, I think it's unlikely to be something that will sort itself out on its own.
Do you have a nice GP? Would it help if you could see a female Dr who might understand the traumatic experience you have had?
I think there are threads on here specifically for women who've had traumatic births and experienced difficulties after, so perhaps start by finding some of those and asking for advice from ladies who have had similar experiences and are more likely to understand your fears and suggest how you deal with them.
Right you HAVE to go a doctor about this. If you can't wee properly you leave yourself open to all sorts of nasty symptoms and infections that could really mess you up. Please see your GP and ask for a referral to a urologist who specialises in problems caused by traumatic childbirth. Take a friend or your mum with you but please get this looked at. Life's too short and too precious to screw around with this.