so could the swelling in my fish be from the worms and not actually be pregnant?

Hi everyone. I have 3 guppys and 1 has developed a rather large stomach so i believe it could be pregnant as there has already been 4 babies born a few month ago so i know theres a female guppy. (didnt notice the pregnancy last time as im just new to owning fish and noticed a little baby swimming near the filter then found the other 3 which i took straight out of the tank). Anyway after spotting the big belly i went on youtube to see preganant guppies and mine looks similar so I have put this fish in a seperate tank as i believe there would have been more babies last time but as i wasnt really expecting any babies some could have been sucked into the filter or eaten. last night this guppy was pooing loads and then i noticed 2 red strings hanging out which dont seem to dislodge when the fish poos. I actually thought it might of been a sign of pregnancy and once the strings dislodeged then the babies would come but iv googled it and people are saying it could be a parasite. also at the minute some of the stones in my main tank have turned green even though i have a filter and bottom feeder fish so could this be causing a problem.