new dog owner

Hi,
I've just come across this website and i think it's great!

I've grown up with dogs my whole life but I personally have never owned one until recently!
We brought home a Shepherd Mix on Friday and I’m a bit worried about her. Wondering if all you dog experts could give some advice.
We got Sydney off a farm and she was not cared for very well. She is the runt in the litter (sisters are twice her size). She is 13 weeks and she was given a relatively clean bill of health.
We were aware that she would have worms (due to the environment she was in) and has had her first round of shots last Friday. Ever since then she has been pooping out the worms, which I’m told is a good thing. How long is that supposed to last?
I thought we would have our hands full with a 3 1/2 month old puppy but she seems very sleepy and docile. I'm not sure if that's just her personality or if something is wrong. When she is awake she seems to play. Not aggressive or hard though. She is a huge cuddle bug and loves being held.
I'm a bit of a worry wart and don’t' know if i need to be concerned or not. She is scheduled to go back to the vet in 2 weeks for further shots. Should i just wait till then to ask the vet?

Update:
I took Sydney in to the vet. She was continuously becoming more withdrawn and lethargic. Good thing I did! She had a temperature of 104 and was dehydrated. She has been in the animal hospital overnight and is doing somewhat better. (Temp down to 102 as of late last night)
Her white blood cell count was so low her immune system was not working. The farm that had her previously was not taking care of her and feeding her improper food. The living conditions were disgusting. We are so lucky to have her in our lives! She is expected to make a full recovery!

Hi Cher sorry missed your post yesterday ..
It sound like your puppy may have been overloaded with worms, this and the fact that she is so young makes her susceptible to infection. Hopefully as she grows stronger in your care her immunity to infection will grow too.

I am so pleased to hear Sydney is expected to make a full recovery I hope you have many happy years together.

Ps Because she has had such a bad start I would feed her four small meals a day of a good quality food to begin with to build her up.