Pregnant fish! PLEASE HELP ME! I HAVE NO IDEA WHAT TO DO!?

i have two little orange/pink fish that i bought off the street and i put them in a small container. i go away for vacation and come back to one fish with a big belly that is sort of black tint to her belly(because you can see through is because it is skinny) and one that looks normal. i have not been feeding them a lot and i think she might be pregnant! i also notice that they will not leave each others sides and are always following each other now... i have no experience with pregnant fish and i have no vets to go to, could someone please tell me the symptoms of pregnancy in fish and also what i should do... please help! p.s- i have her in a gl cylinder cup like thing with no plants or little pebbles at the bottom... should i get some of those? sorry i have no experience at all!!!