Don't rush also if someone is interested in you they will stick around and holla at you often, the only way you can tell if a girl likes you or something is don't text them like next morning and see if they text you within the whole day if they do choose a subject and talk about it or just start a convo that will never end or properly will.
How i know if a girl likes me on whats app i have this chick shes pretty HAWT no lie me and her met at westfield and she came up to me asking for my number so i gave it to her after that she kept texting me everyday so i stopped texting her for a day around 2 in the midnight she texted me with heart and shit lol. Just give her time or something she might be going through a break up or hard times just wait up mate, also try not to bother her too much or be annoying because i know some lads can get abit annoying at times.