Well, my advice would be to put your big "anonymous" panties on and do what needs to be done. As you get older, get a job, and live life, you will be doing many things you don't want to do....because you have to.
I have been feeling stressed and even depressed lately. I have a piano concert coming up and my teacher is giving me heck for not being so ready... but I am! Also I have swimming lessons I HAVE TO DO and I HATE THEM!! Help?
I get this feeling these two activites are something you earlier enjoyed doing, right?
Until the events have passed be sure to get plenty of sleep, & just for now limit any other activities. Meaning for right now friends-wise
not being too available. You don't have to answer all text messages for example, so tell you friends this is just for now - you can always be your friendly self later on. The knack of focussing doesn't come all by itself . :-) and you need to do your best at what you're good at.
If you don't have a choice on the swim lessons, just remember how long they are (say, you have to do them for another 5 weeks), so you can see the end is near. If you don't know how to swim, the lessons are a great way to learn so you're not fearful in water. If there is another goal in mind - say your mom wants you to be on your school's swim team, sit down and talk to her about her vision and tell her how you're feeling about this.
Don't be rude about it - just talk to her about how you're feeling and see if there is a compromise you guys can come to.
On the concert, this is a reflection of both how prepared you are and how well the teacher gave instruction so they are nervous for you. They want their students to do well.
Again, don't give a snarky response back - just tell her that you've got your practicing in and everything will be good. And then show her how well you've done. Good luck.