I cannot recall who supposedly said that greatness is 1% inspiration and 99% perspiration, but they had a point.
Working with myself and with many others, I've realised that it's far easier to feel confident in something when we have learned, practiced and begin to let our authentic selves shine.
So never stop studying, reading, trying new things, practicing, and growing.
Lack of confidence saps your belief and willingness to experiment. But trying new things, conversely gives you richer experience and more to build on.
Look for inspiration wherever you are. Can you find someone who has something to say on your subject that you can learn from?
Here are a few tips on public speaking that may help you. https://www.facebook.com/businessinsider/videos/10153710650269071/
Please let me know what's been inspiring you lately.