I put 'I am also here' for the translation into English. It rejected it. Can you explain why, please. Thanks.
'też' means 'as well'
'zbyt' means that there is an excess of something (e.g. 'Jest tu nas zbyt dużo' - 'There are too many of us here')
No. In fact, it's 'after the subject' here, because you can treat it as "Ja też tu jestem!" Another common option would after a verb: Zrobili też zupę.