Probably. You need to give your body time to recover.
Through your teens and twentys I think it is quite normal to wank-off several times a day. But as you have noticed, the more often you wank, the less fluid you will ejaculate per session.
Orgasming without sperm/semen is a perfectly common phenomenon, nothing to worry about. It's simply that your body can generate sperm and semen only so fast, but you have the ability to have orgasms more frequently than that. The orgasm is still an orgasm, regardless of whether the "Eject!" function actually has anything to... eject.
That doesn't mean you're masturbating too much.
Or to rephrase: THAT doesn't mean you're masturbating too much.
Independent of THAT, there's the "how much is too much?" issue... well, 8 a day is well beyond any friends of mine's personal records! I know of guys who can manage 5, but that's an event like "I was trying to set a personal record!", and then afterward it's like: "Wow, okay, new record. But... never again." Normally, 3 means "okay, now time for a shower, a sandwich, and a nap."
I'd say: "too much" masturbation is: Is it interfering with your ability to do other things in your life?
But I have to say, and don't take this as condescending, but: for 16-year-old boys, at least like I was, I'm amazed they find the time to do anything *but* masturbate.
But also: some guys can, uh, "go from 0 to 60" in under a minute, or two or three. If you can do that, and that 8 times is just something you can do for three minutes every few hours, well, I see no harm.
To test if you're doing this addictively/compulsively: try a rule of "3 or 4 times a day, never 5 or more!" and stick to that for a week or so. If you can pretty much stick to that rule, that's a good sign this isn't addictive/compulsive.
A lot of guys can use edging to kinda halfway orgasm several times, in a single session, and they might stretch that session out for 45 minutes, so that could bring your count to 4 to 8 total. By edging, I mean: a few seconds before you're about to orgasm, you stop and... hold back. But it's actually sort of having a kind of muscle coordination that I never got until I tried some Kegel exercises. But some people are naturals at it. (But if this is the first you've heard, you can google on it, but don't go doing 200 reps right now, or you'll *ache*... these *are* muscles after all. Space it out over the course of two or three weeks, so you'll be up to speed in no time.
In any case, being 16 might mean you wouldn't quite have the coordination/practice/restraint to manage that, or you might not like edging as much as just a straight full-on orgasm.
OR it might mean you'd be extremely good at it, and might especially enjoy it. Everyone is different-- and everyone changes over time.
A final consideration: "too much" masturbating means:
* If you've got an ache (anywhere) from having an erection for too long, but if you still keep at it, that's an operational definition of "too much".
* If all that action is irritating/chafing the skin, then you're doing it too much,... or at least you need more/better lube.
You *better* be using lube! If not, scrape together some pocket change and go to a drugstore and buy a small bottle of Astroglee or whatever it's called. Embarrassed? Who cares. The clerk at the store doesn't care. All he/she will be thinking is "I wish I had been brave enough to buy lube when I was young as this guy" and "when do I get off shift?"
(And do NOT try using something non-lube as lube. It'll just irritate your skin, especially the tip of the penis.)
Everyone has their own particular favorite texture of lube-- that's why there's dozens of brands/mixes in the drugstore. If the texture isn't quite right, or if the texture changes after a few minutes, a few drops of water can change that.
PROTIP: lubes with silicones in them will generally leave stains, but water-based lubes generally won't. Read the ingredients lists online. Basically anything ending in "-one" means silicone, even if the label doesn't say it in big letters on the front. Really, this is a big consideration, for stains, and for texture.
Now go have fun! (You're welcome!)