Lump on left side of neck, a swollen lymph?

Yes, it could be related to being tired lately. If you were ill two weeks ago, it could be something that has not gone away -- you feel fine, but whatever bug caused you to be ill is still there. If it is an enlarged lymph node, you definitely want to have it checked a.s.a.p. Tell your parents about it right away. You need to see a doctor or nurse practitioner.