I have a seven month german shepherd puppy who to my horror has worms.
They're deffinately round worms probably ascaris and they're huge- by my worm standards anyway. I went to the vet on Monday and got dewormer which I promptly gave him when I got home. After I did this he started itching like crazy (I should probably mention he's been itching like crazy for the last two months- worms I think? Though the vet said allergies... it's not like they tested). Anyway, he didn't go to the bathroom except once on Monday and then today he went in the morning just a little and there were worms in his stool but they were still alive! Now he won't go to the bathroom still and he's still scratching like mad. I gave him another pill today and I have one more for tomorrow... but aren't these dewormers supposed to act fairly quickly?

I live in Poland so this is making the whole situation even more frustrating because the vets here seem to be incompetent! He was treated for worms in February, but never given a follow up pill for the eggs. In fact they never tested his stool in the first place like they do in the US. On top of that like I said he's been scratching and biting at himself and I've eliminated almost everything from his diet with no luck- but they haven't tested blood or made and real query's about it!

So the real question: how long should the pill take to work? And what do I need to know the next time I go to the vet?

I guess that would depend on first what medication they gave him.
And second, that it is the proper dose for his weight.
Speaking for what is typical in my area.
For an infestation, he should have three days of medication, then in three weeks another three days of medication. (because of the life cycle of the worm)
Some vets prefer to retreat a third time in three weeks to make sure the pet is clear and then testing the stool in a couple weeks to see if there are any more eggs.
A puppy would need to be weighed before each treatment to ensure proper dosage.
It is also helpful to know exactly what parasite you are dealing with by means of a fecal exam.
Roundworms look much like spaghetti, so if you are actually seeing worms then that is probably what you are looking at.
Tapeworms can also bee seen with the naked eye, they look like a grain of rice.
Hookworms and whipworms you will not see.
I can't explain the itching after taking the pill, unless there is a filler of some sort in the pill that is affecting him.
The dewormers we use are a liquid form, so I'm not familiar with a pill form.

And of course I'm sure there may be parasites in Poland not found here.

As far as the itchiness goes, I thought I understood that they did a scrape and had to send it to an outside lab or something, I may have misunderstood, but I assumed they were working on this problem.
Did you try the benadryl to little avail?

Haha... Trust me it's roundworms- I've never been quite so disgusted in my life. I confirmed it with my parasitology professor who unfortunately can't help much seeing as he's a dog.
They did the scrape and it came up negative. He's eating dog food that's basically just fish and whatever else they put in it. No eggs, no wheat, no corn, no rice (it took me forever to find that combo). They did check his weight before they gave it to him and I have one more pill for a total of three. It looks like the pill is praziquantel... which was used during his last worm issue (but I only got one pill then).
The benedryl seems to pacify him for about an hour but after that it's back to the same old thing. I'm going back on Friday to go for what they called "allergy control" which I assume is just more cortisone. I know that it will make him feel better, but I'd rather treat the issue as opposed to the symptom. But, it looks like I'm going to have to get him to look good enough to get on the plane and through customs so I can take him to a real vet.

Thanks for your help!

Ah, OK so probably something like drontal plus, which is a broad spectrum, I was thinking on the lines of synathic and strongid, a liquid dewormer.
Drontal plus also kills tapeworms whereas the liquids do not.http://www.marvistavet.com/html/body_praziquantel.html