Random ideas that occur to me on the topic, not knowing you personally, but having a lot of sympathy for you. I’ve had similar experiences.
I suggest you re-focus your objective to making people enjoy talking with you, instead of finding interesting things to say, and showing what you know.
Try talking less, and listening more. Aim for speaking half as long as your partner. Ask more questions, even if you may know the answer, to let your conversation partner expand on their interest. Google and research “active listening”. Buy books on it. Heck, do a search on it on this board. Master it. It will improve how you relate to your co-workers, your spouse/lover, and even your children. It is the closes thing to a Jedi mind trick to defuse mad people who are screaming at you, esp. customers and significant others. It can save marriages. Yes, it’s that powerful.
Let your conversation partner talk about themselves. Everyone loves talking about themselves. If the conversations flags a bit, then you can take out some of the knowledge you have, but use it to set up a question to your partner about themselves. Try to pick a topic you think the person is likely interested in, or one relating to something you have in common.
Aim to improve your understanding of people’s body language. You can do this through books, courses, and web sites. This is way more important than you appreciate right now. Learn to read what other people are saying, but, more importantly, find out what messages you are sending as well. A course I took (was sent to by my boss, actually) showed me I stood too close to the partner (looming over them), faced them too squarely (confrontational) and spoke too loudly (also confrontational). Implementing what the course people said felt so fake at first, but it totally changed the way colleagues related to me. It was like they had all been reprogrammed to be nicer, to listen to me more, and to not reject what I was saying anymore. After a week, I was almost weeping at the “injustice” of not having known this 10 years earlier, when I was starting out in the world.
Use your body language to convey openness and interest, that you enjoy listening to what the other person is saying. At the same time, watch for signs of boredom like closed postures, looking away, and interest in fiddle toys. If you see them after you’ve been talking a while, STFU ASAP, and make them talk instead.
I think the frustration you feel results from trying to improve the wrong dimension of your conversational skills. It’s not your knowledge base that’s the matter, it’s the *manner *in which you carry out conversation. I hope this helps you.