It is okay to be uncomfortable or scared or nervous or angry about having to ask someone to pay you. it is an unfortunate reality. give yourself a moment - just a moment - to be uncomfortable, grossed out whatever. then get over it and get paid.
the best advice i ever received was to negotiate my pay as if i were negotiating on behalf of my best friend. whaaaaa?!?! this was mind blowing. i would have no problem gassing up my best friend's accomplishments and telling anyone why she deserves a raise, more money, a promotion, whatever the hell she wants. she works for it, she's earned it.
and so do you.
the easiest way to avoid the conversation to be paid after you've done the work is to have the conversation upfront. when you are starting work (assuming you are a freelancer) make it clear - in writing - what you charge, what you are going to do, when you are going to do it, and when you expect to be paid. and what is acceptable in terms of communication. do not allow someone to blow up your phone or email with requests and "needs" at any time. do not allow people who have hired you to cross those boundaries -more on this in a moment.
if you don't get to have the "up-front" talk or are currently in a situation where you are waiting to get paid, i have a few ideas...
set up a billing email address - this way - the "billing" team is handling the finances and uncomfortable convos... you can hide behind an email address and be all business. there is no need to have a face to face interaction. Set up an online payment system. Even if it is just to a PayPal account. Use email@example.com for any set up and your clients (whoever) knows they are paying your business, not necessarily you as a person.
need face to face interaction with a client? hire someone for a day to be your billing coordinator. not a joke (i, personally, would be happy to do it.) Create a billing team and let them take on the grossness for you. Again, happy to do this, I charge one meal, preferably dinner and a bottle of wine. See, that was easy - I am offering you a service, and you know what I expect to be paid for that service. And you're not mad at me! You want to hire me to make your life better. done. deal.
Moral of the story - get.paid.