Weakness standing up after a few minutes is low blood pressure or sugar levels; something blood related anyway. I have such low blood pressure even stretching or sitting up makes me feel like I'm going to faint, let alone standing up. You haven't mentioned any symptoms of a brain tumour, so how can it be a brain tumour?
The ear thing could be anything, it wouldn't be linked to a brain tumour. Maybe you just have an ear infection? Have you been to the doctors? I had this scare of a tumour a month ago, and it lasted over a month. Turns out it was just major anxiety.
Trust me, if you had a brain tumour you'd be having bad headaches in the morning, being sick, memory loss or some kind of "special symptom" depending on where it is in the brain, eye problems (doctors can spot this) and the symptoms usually get progressively worse over time as it grows. If you haven't seeked any medical attention yet, then things can't be that bad. If this is worrying you a lot like it did to me, just see a doctor, they should help put you in a better and more positive state of mind.
Get better soon, and good luck!