I bounce back and forth also. Usually i am sort of 'beyond' feeling, other times i am so hyper-emotional that i feel like wailing child (inside, of course). I believe this is totally normal for certain people, and somewhat changeable through a variety of means (therapy being what helped me the most, though I still struggle.
I think a literal 'empty' feeling can more accurately be described as a dissociative state or distancing from emotion, perhaps purposefully and/or sub-consciously. There is a lot of information on dissociative states around, generally the consensus is that most pathological dissociation is a result of emotional trauma of some kind (the most benign of these being something like teasing at school), also things like witnessing a parent/sibling/friend die and feeling like you need to be "strong" and not show emotion. Again, no one taught you how to do this, it's very natural under many circumstances I'm sure, not limited to those I've described. But honestly how you got this way is not that important imo. Of course all of this is my opinion btw
Feeling so numb inside that pain is preferable to nothing, will land in you in a whole lot of trouble namely by destructive compulsive behavior. Drug addiction, eating disorders, kleptomania, self harm like cutting/burning... all of these give an intense rush of some sort, easily confused with emotional outpouring and sometimes hard to self-limit. What I mean is, many people including myself cycle through some of these behaviors in an attempt to feel, like you said *something* as opposed to *nothing*, and so now I am a hamster on a wheel (or cycling between several wheels) because it gives the illusion of control and emotional response, otherwise I am even more dead emotionally than I used to be. The result is stagnation.
I didn't live a typical childhood at all, and I don't remember most of say 14-19 (didn't do drugs until 19 incidentally), but it is my understanding that some of this is normal. The desire to go beyond the limits of your personal psychological defenses (like numbness) is natural and in healthy people this turns into healthy risk taking... perhaps something like LSD or mushrooms would be a good experience at this point... "cheap" highs like meth/opiates/coke etc. seem counterproductive to a healthy life for many (not all people). Not to mention your brain is still developing, and you don't want to become a mentally unhealthy adult (believe me).
I'm just kind of rambling at this point, but I wish I understood my kind of lot in life at 16 years old. Take some healthy risks, have wild sex (with condoms!), hell go to therapy (good way to feel something eventually, it even worked on me), learn an instrument. Taking drugs for a chemical reaction that makes you feel "good" is okay but it's not the answer. Then again you will probably try most classes of drugs in the next few years, so have fun. Opiates are especially hard for me, I can really get emotional on them which can be addicting in itself for someone who is usually numb (as you have already picked up on obv with this thread), and generally I feel just more comfortable physically, mentally, all around. But after about five years they don't work so well anymore, even occasionally as I have not been seriously physically addicted in a few years.
and yeah I know drugs will only work for so long, it's just when I feel that down and empty I don't care about anything else all I want is to feel something even pain, just something to make me feel like I'm actually a human being who can feel emotion. 
