Dalmation Molly Problems

I have a 2.5 gallon fish tank that is sparsely furnished. Within the tank is a Dalmation Molly, a nonaggression betta fish ( keeps to himself) and a Cory catfish whom reminds at the bottom of the tank. Well I recently got these fish bed we set up the tank and decile oater the water. I guess you can say that on Thursday I noticed that my tank was nasty so I did a 100% water change. Place my fish in separate tubs and dechlorates that water also. I cleaned the tank, plants and gravel with just plain water, no soap. After that I set everything back up and filled the tank up with water and placed at least 14 drops of water in the tank since the directions calle for 7 drops per gallon. I let the water sit and I took the waters temperature. It was 76F I believe. Then I placed the tank back in my room and placed the airator in it. I added the fish and everything was going smoothly. Well last night I noticed that my Dalmation Molly whole I named Bait had been acting strange. She swam in place for 15 minutes doing a snake like motion. I went to sleep an when I woke up this morning she was in the same general area same motion. At the top of the tank. All my fish keep to themselves. Every now and them my Dalmation will chase the catfish an bump into the betta but that is. Well just a while ago I noticed a white almost clear string dragging from her anal area. What is this? Could she be sick?

My Dalmation Molly

Do you use a dechlorinator when adding new tap water?
Does your tank have a filter in it?
Have you cycled your tank (if you do have a filter)
You shouldn't really do a 100% water change as it can shock the fish, just do a 60% change max.
How much and what do you feed them?

I fed my beta and Dalmation Molly a pinch of this once a day or every other day due to tendactbtjat I occasionally find some floating on the top. The blood worms.

Yes I use a dechlorinator.

I do not cycle my tank

I drop a least three to four of these in various areas around the fish tank for my Cory catfish.

It probably isn't the cause of the problem, but try feeding them a flake as well as bloodworm. And if you don't already have one, a filter is quite important in maintaining a healthy aquatic environment (and they're not that expensive)

You have stocking issues.
Dalmatian mollies need better than a 2.5 gallon. So do cories.
Get a bigger tank or rehome the mollie and Cory.

Sorry, mate, but your tank is way too small for those fish.
 
Do you know what "cycling" is, because it sounds as though you don't?