This is going to sound totally Life Science, but...
When you're 17, so much is changing (hormonally, chemically, emotionally, physically) that it's not surprising to feel anxious and depressed sometimes. What is important is to learn to recognize the severity of your feelings, and deal with them in a positive way.
What exactly are you anxious about? Just your relationship with your boyfriend?
Or do you feel depressed in general? Hopeless? Frustrated?
It's difficult to give you a more detailed response without knowing exactly what you are experiencing.
Regardless of what it is though, there are a few things you can do to relieve tension/depression in your life before deciding to see a doctor.
(1) Exercise. 30 minutes or more per day has a seriously miraculous effect on your mental health and well-being. It sounds like bullcrap, and I scoffed at my shrink when I was told that at 16, but it's true. Going for a short run, biking, or swimming laps will all perk you up to some extent.
(2) Diet. Eat small meals throughout the day, and drink plenty of water. Try to avoid sugar, caffeine, and cigarettes. They can all make you feel edgy.
(3) Socializing. You seem like you've got a fairly stable social life going on, and this can also be a positive thing.
Try to remember that, while you may feel isolated, there are always people who care about you. Being 17 is hard, and there's no reason to beat yourself up about the little things.
Best of luck, hon. <3