Question: Could I possibly have a brain tumor?

Some of the problems I'm experiencing have been happening for years, while others have emerged within the last few months/weeks.

Years: Inability to concentrate or focus. My mind wanders internally (if that makes sense). I'm not distracted by a picture on a desk or a bird outside the window or anything like that. I just casually shift from one thought/topic to the other, and I frequently don't even realize what I'm doing until a lot of time has passed.

Also within the last two months I've been diagnosed with ADD and depression. On medication for both. (ADD meds don't seem to be helping)

Months/weeks: I cannot understand hardly any information the first time I see/hear it anymore. When reading, I'll read each individual word, but nothing clicks. It's as if I'm looking at a scrabble board or something...it just looks like arbitrary nonsense. Takes several tries to put together what I read and understand it. I'm also having some problems processing information via listening. There could be absolutely no distractions around while I'm giving someone 100% of my attention and I'll still have issues. It's almost as if I don't hear them. I know something was said, I just have absolutely no clue as to what it was. It takes a few seconds to process, so if I have time to sit there like a doofus then that's fine. However, if it happens during a lecture, then I'm screwed. I miss one sentence, so I try to think about what was said and get the information I missed. Meanwhile, I just missed the rest of the lesson. I also have awful balance/coordination recently. Granted, I've always had poor coordination, however, I can't even go down the stairs without leaning my entire body against the wall, or having both hands along the walls while watching my feet hit every stair. And if I'm not watching the ground as I'm walking then my feet will cross over each other and cause me to fumble.

(Paragraph became way too long, below is months/weeks-continued)

Headaches have become very frequent, while ranging in severity. Some mornings I wake up with an excruciating headache and with my eyes and ears very sensitive to any light and sound. While on the other hand, I could simply have an unpleasant throbbing in the back of my head throughout the day. I get light-headed/dizzy very easily now as well. Simple things like sitting up, standing up, going up the stairs, putting my chiropractic head weight on, turning my head, etc. Blurred vision and/or seeing spots usually accompany the dizziness. Also, I'm not sure if this has to do with memory or not, but I have been mistaking numerous events or conversations that happened in real-life for dreams.

And some background that may be relevant is that I have a reversed cervical curve that is off by about 65° in total. (-20)

My mother keeps making jokes about me having a brain tumor or bone cancer (due to separate issues), so I'd just like to know if that can be ruled out or not.

And I almost forgot to mention that I am a fifteen-year-old female, that is usually a very good student (AP and Honors classes). However these recent problems have been causing my grades to drop drastically.

Thanks to anyone who takes the time to read and respond! :)