Flat is just not beer......

I'm fairly new to home brew and encountered a problem. Made a heffaweissen via extract kit. Made a yeast starter with Wyeast Bavarian Wheat. Good activity in the starter. Couldn't boil until about 48 hours later. Pitched at below 80 degrees. Good Kreusen. Moved to secondary for about 2 weeks at 70 degrees. Then bottled using the standard priming pack of sugar in the bottling bucket. Now in the bottle for nearly 3 weeks and it's completely flat. Glass bottles with standard crown caps so I'm confident of a good seal. No off tastes though it is my first try with this one and I don't have a baseline for how it should taste. I did forget to take a final gravity reading so I'm not sure what that was. I have no clue what went wrong or how to fix it. It's as if the yeast died off. I did open 2 last night-added one Cooper's dextrose drop to one, two to the other and recapped. We'll see...
Anyone with similar experience or thoughts? I could open the bottles and re-innocculate with dry yeast or just learn to enjoy it flat.....
Thanks for any help.

Did you leave the bottles at room temp for 3 weeks?

Do you know how much sugar you added when bottling?

Did you see any co2 bubbles when you poured it in a glass?

It could be just slow and maybe it will carb in another week. That's usually how it goes for mine.

Bottles are at room temp. About 3 weeks in. No bubbles at all. I actually boiled 10 gal-split the batch into 2 fermenters: one got the Bavarian Wheat strain, the other got Weihenstephan (sp?) Both starters, fermentation, secondary and bottling were side by side and the Weihenstephen batch has done well. Well carbonated in the bottle and tasting good. The Bavarian Wheat strain of yeast on the other hand has been a different story.

Is there any sediment in the bottles?

Kind of a pain, but I'd put a few grains of yeast (US-05 is a good choice) in each bottle and re-cap. A flat wheat doesn't sound good.

You really need to use a priming sugar calculator to figure how much to use. The right amount depends on how much you want to carb it, the temp of the wort, the OG and FG, and the volume of beer you're trying to carb. (Among other things.)

And hefeweizens seem to be finicky for me. I still haven't hit the sweet spot on those.

To SocalNat: checked last night-yes to sediment.
The priming sugar calculator is an interesting thought. Where do I find one?
Unless hef is indeed that finicky, I wonder if I just messed up and didn't get the priming sugar into the batch. Rookie error vs. senior moment vs. home brew brain or a little of all of the above??
I do appreciate the help.

Try adding the yeast as suggested, or try in a few bottles and see if it works before replenishing 50 or so bottles with it. Did the bottles you've tried taste a little sweet, as if there was priming sugar that didn't ferment? Or did it not taste sweet at all and maybe as you suggested you forgot to prime?

As a last resort, and I did this myself on a flat batch, put it into a keg and force carbonate. This assumes you have a keg of course, which if you are bottling you probably don't.

Or I have an even better idea: Ship it to me and I'll keg it for you, and drink it too!

I am really not a fan of those priming sugar calculators. It seems like they are not really good for giving good carbonation, because they carb "to style". Well, most bottled beer that is purchased commercially isn't carbed to style- most of us are used to a certain carb level. The other thing that concerns me about some of those priming calculators is they say a hefeweizen should be carbed to 4 volumes of c02. Well, maybe so for a kegged beer (it'd be very spritzy) but for a beer bottle that would be more like a bottle bomb which really is dangerous.

I normally use 1 ounce of priming sugar (by weight) per gallon of finished beer for most beers. It works great, and I don't have any carbonation issues.