For most of my life I struggled with communication. Without getting too deep into my life story (haha) I’ll just cut to the chase and give you some advice.
Write it down (or type it up). Read it out loud. Delete it (throw it out). This process is so therapeutic because it helps me sort through the garbage my ego creates. So then I can find the accurate words and phrases I need to express myself.

Be kind to yourself when and if you clam up during a stressful conversation. Take a few deep breaths and use body language to express to the other person that you are indeed listening to what they’re saying. I find that a lot of the time people don’t actually care if your engaged in the conversation. They just want to feel like they’re being heard. If they are giving you a hard time about not being ‘engaged’ in the conversation just tell them that you’re much better at listening. Don’t consider your lack of verbal sharing a bad thing.

Instead of telling yourself “I am bad at communication” tell yourself “I am a great listener”.

On a final note, people are going to say some pretty crappy things to you throughout your life. You have to let it slide off your shoulders. When that dude told you that “nothing you say holds any weight” it really hurt you. Who you are and what his perspective of you are two different things. (As is the truth with every person on this planet) His opinions or views of you have nothing to do with you because it’s just part of the story that he tells himself everyday. You are only a secondary character in his life and visa versa. You don’t have to make his words your truth. You make your own truth.

Bottom line and my most favorite piece of advice: Be nice to yourself. Talk to yourself like you would your best friend. Once you do that, so many more positive changes happen inside of you.
(I highly recommend reading The Four Agreements by Don Miguel Ruiz.)