Fish help

We just bought 5guppies 2days ago..

2died yesterday and 2 died today... the last one seems like its probably wont make it either im devastated 😪yeah there fish but they were my pets what probably went wrong..i spent so much money on getting a 20g tank and than buying alot of stuff. .. should i get guppies again or what other fish

edit... of course I researched and read about them... and got everything that was needed for them...