Help with identifying this little guy's sex

[gary44]

Hey everyone im new here
I have this little guy for 2 months , since he was about 3 cm. Now he's about 8 cm and i've heard him croak a few times ( late at night ) but sometimes he looks like a female and i don't know if he's growing fast enough for him to be a definitive male.
These are his current photos :


And he has cool temperatures since the weather here in Poland is pretty cold ( in his tank it's about 21-23 celsius ). Should i heat his tank and if so what do you recommend for that? Help appreciated! Cheers