Whats wrong with my Molly fish?

Question:

Ok I have a 2.5 Gal starter kit aquarium. with some neat decorations. PLENTY of room for my Molly to swim. It is filtered and I have a heater in it. Water temperature is 78 Degrees. I have no idea about the water. I know I changed it today. I put conditioner in the water and let it cycle for 30 mins before I put my Molly back in the tank. But today after I changed the water my Molly started acting weird. It laid around the bottom and then every once in a while would like Swim all around the tank and try to jump out of the water then it started like gasping for air. I thought my Molly was dying but now its kinda calmed down A LOT. but how do I know if my Molly is a male of female, and How do I know if its really ok or if its still dying :( I really gotten attached to Mollie... thats its name :) and I really dont want him/her to die.

Answers:

they dislike water change... id need more details to know more but it could just b shock.

If you really care about your mollie, you'll either buy a bigger tank or take it back to the pet store where you got it.