Howdy! I'm in need of advice

Sorry to hear of your loss.
It is very hard to determine what illness/disease you may have. With that many birds dying in a short period of time, the best way is testing.
Can you take one to a vet?
I highly recommend you send one for necropsy.
You would need to find your state vet for necropsy, but the following link shows how to send it:
https://www.backyardchickens.com/t/799747/how-to-send-a-bird-for-a-necropsy-pictures

Can you provide more info?
Do you have photos?
How old are they?
Are they layers or meat birds?
What type of feed/treats do you use?
Explain lameness?
How long had they been showing symptoms?
Any other symptoms, wheezing, distress, runny nose/eyes, discharge, etc.
What is the timeline in the 3 deaths? (Days, weeks)
Did they all die from the same symptoms?

Here's some info on Common poultry diseases:
http://edis.ifas.ufl.edu/ps044
https://www.backyardchickens.com/a/the-great-big-giant-mareks-disease-faq

Some causes of swollen abodomen:
http://www.chickenvet.co.uk/health-and-common-diseases/egg-laying-issues/index.aspx
http://scoopfromthecoop.nutrenaworld.com/tag/laying-issues/

 

Chickens with ascites or water belly can have amber fluid flowing freely in the abdomen. That is common in hens with internal laying and egg yolk peritonitis, but also can occur with heart or liver failure. Internal layers may also have problems walking due to pain, may walk upright or like a penguin, and can have runny droppings or pass cooked egg material in droppings. Some of the links that Wyorp Rock has provided above can explain some of that. The state vets in many states will necropsy a chicken after death to look for a cause if you have another. Sorry for your loss.