I'm sorry your grades have been declining, but I'm not sure "laziness" is the only issue... It might be helpful to think about what else, if anything, is going on in your life right now.

You seem really focused on getting straight A's. I wonder whether this is an expectation you have set for yourself or whether your parents are pressuring you to get perfect grades. No matter where it comes from, it may be really hard to concentrate under all that pressure.

Adopting a more gentle approach might help. Calling yourself "lazy" may mask other problems that you can deal with. For example, you said you often feel "overwhelmed" and "tired." Is that a new thing? Are you feeling okay physically? If not, perhaps you might talk to your parents about seeing a doctor.

Has your coursework changed? Are you taking subjects that don't come as easily to you as in the past? If you need help, talking to your teachers can really make a difference. They may be able to spend some extra time with you on the subjects you find most difficult. Or they may know of other students or teachers who would be willing to tutor you.

Feeling depressed or anxious could also account for your sudden lack of motivation. Have you been down in the dumps lately? Do you find that you are too distracted to concentrate? That wouldn't be surprising, considering your everyday concerns and what's happening in the world right now. If this is the case, talk to your parents or your school counselor or some other trusted adult about getting help to pull yourself out of the doldrums.

Don't be too hard on yourself!