This is a pretty common problem and it is because often you can wait until the last minute and then get homework done and still complete it successfully. But if you develop that habit and then run into a situation where that may not be possible, it is important to develop study skills that can help you take it all on.
One key to being able to take everything on is to be able to break all of your work up and then focus on one thing at a time. Try to get one assignment done immediately after school and then do another assignment before bed. If you do this each and everyday, it should be easier to keep up with everything. If need be, it may also be good to get up a little earlier and also complete an assignment before you head out the door for school. You need to set up a schedule and then stick with it.
One thing that can help is to reward yourself each time you get something done. For example, turn off the phone and internet until you get your assignment done. Than after you are done with an assignment, allow yourself those things again. You could also do this with television shows or music. How you restrict and then reward yourself will be up to you.
It's not easy and it does require some good self discipline, but once you start the habit, it becomes easier to maintain and your life will be much less stressful overall. If you find yourself continuing to struggle with either the difficulty or amount of the homework over time, than it may be important to talk to somebody at the school about keeping up. Maybe a tutor or a homework group at school would be useful in getting things done.
You could even set one of those up with your friends, but you would have to make sure you worked on homework and didn't simply socialize, which can be hard. We wish you well and hope that through scheduling time and focusing at one thing at a time, this becomes more manageable!
Please take care and let us know if anything else ever comes up!