Molly Is Laying At Bottom Of Tank

[KMA1225BKW]

I have a Dalmatian Molly. I have had it for a couple days now. I did a water change today and checked all my levels and everything was fine. I have 2 Dalmatian mollies, a male guppy, a male dwarf gourami and 2 blue gouramis. After I put them in the tank the one molly was laying at the bottom on its side. I thought it was dead but then it swam away but went right back to the bottom. Not sure if its a female or not but the belly is alot bigger than the other ones. Also it has red by its right fin. What is wrong with it?

 

[nic1]

How long have you had your tank for?
WhT are your water readings?
Has it always been Ill or just after the water change?
Is your water hard or soft?
We will try and help, don't worry.

 

[attibones]

The questions above are helpful. Would like to add a few more:
 
How large is the tank?
What products do you do during a water change?
How much water is changed?
What's the temp?
How long has it been since the last water change?
What test kit do you use?
 
Red on the fin could indicate many different things such as aggression related injury (likely considering dwarf gourami can be nippy), a breeding accident (males can harass females), could be injury caused by decor, ammonia burns (or is it nitrite which shows physical burns? I can't recall), internal hemorrhaging, etc. Lying on the substrate may indicate poor water quality, lack of 02, or stress.