You're definitely not alone Ellen. I really see myself reading your post. Anyway I already meet this problem in an other domain (webdesign) some years ago, and I learned that time and practice (a lot) is the key.
We often tend to be frustrated, even more today because we can see all those talented "pros" like you said, sharing their creativity and totally forget it's often the work of a life. Personally, when I take a look at my instagram feed or even a calligrapher's website, it's like a big kick of motivation: "Oh yeah, that's why I'm spending all this time in this practice"
Anyway for me, (1 month of practice, more or less 1-2h a day), I have to say it's still really bad for now, I mean, no straight lines, no beautiful flourishes (Erica keeps her flourishes video secretely
), nothing pro. But if I look at the work of the previous weeks, I see some changes (good ones).
I think calligraphy is all about this, a lot of time and self-infestment. Slow, hard but well rewarded efforts.. at the end (if there is an end, probably not)
I think it's more about an apprehension than something else, don't discourage yourself, be sure to get the good tools, the good position, the good paper, and you'll improve your writing for sure. =)
Maybe share a pic of your writing or problem here so experienced calligraphers can tell you obvious errors and any other suggest to improve your work!
I'm not so much on number today, for me something really hard is letter-spacing. That's what I'm focusing on these days =)
Anyway I hope it will reassure you, let all this frustration down and believe in your capacity!