It seems that you have a decent IQ. Additionally you seem to be conscious and can avoid procrastination which is a very, very valuable characteristic.
On the other hand you have issues with self esteem. As far as I understand IQ testing gets used by real psychologists in cases like this.
Taking David Burns CBT book, "The Feeling Good Handbook" and doing the exercises every day for 15 minutes would likely do a lot for you, especially if you can get yourself to do the exercises regularly.
I also support Nancy's suggestion of Feldenkrais.
Another stupid question to boot: will all this make me more content with my current situation? While not being a pleasant feeling, my discontent with my competence does serve as a motivator to actually study. I wouldn't have asked this question here and wouldn't receive all the advice if I were less competent than everyone else and okay with it.
This thread is for asking any questions that might seem obvious, tangential, silly or what-have-you. Don't be shy, everyone has holes in their knowledge, though the fewer and the smaller we can make them, the better.
Please be respectful of other people's admitting ignorance and don't mock them for it, as they're doing a noble thing.
To any future monthly posters of SQ threads, please remember to add the "stupid_questions" tag.