What's the best way to stop feeling incompetent ?

Start doing more things you actually love, that will make you feel better, more motivated and hopefully more productive. Or search new ways of doing the same things you think you are being incompetent at.

Appreciate yourself more often. We often forget the best things about us and focus on the worst. Appreciate your best traits, whether it's your patience, your honesty or your brains. We often (as students) label ourselves incompetent due to academic validation. Be proud of your past and use that to move forward. So what if you've only gotten one A in the whole academic year?! Be proud and say "I've had an A before. What's stopping me from getting another one?". Use this same example with every other thing in life. Don't forget your qualities and most importantly, don't let your problems be bigger than they seem!