If I were you I would move this to the freshwater fishdiseases thread! I had a question about my guppy too and got more responses once I moved it there. I hope everything works out ❤ I’m sorry your little guy isn’t doing well.
Is she pregnant? I read somewhere that this happens when they are pregnant. My female, a same kind as yours is pregnant and I see poop like this occasionally. A new male guppy that I bought a few days ago has camallanus, but the female had this kind of poop earlier. I am going to be treating the tank anyway and hopefully the anti nematode, thing that I use will also get rid of any other parasites if that's the case.
I'm interested to know what others have to say about this.