How do you know if its senioritis or depression?

I half-way my senior year in high school and have noticed that I've been having some continuing problems from last semester. Around November I started becoming extremely tired and uninterested in everything, including things I used to enjoy like reading. I went to my doc think their was something wrong with my thyroid (I was diagnosed with Hashimoto's Disease/Hypothyroidism 8 years ago) so I figured that a change in meds would make me feel better. But I have yet to see any changes; in fact its getting worse. I have to set my alarm an hour early just to make sure I wake up in time to get to school, where I used to be an attentive student I now find myself either falling alseep or lost in a daze in almost all my cles, and I have no energy or desire to do my homework. I haven't seen any change in my grades yet, I'm still ranked 3rd in my cl and am managing to keep up with my advanced cles. If anybody could give some advice it would be very helpful.