Just bought my new MacBook Pro 2 weeks ago and gets really hot when using it. WHY?

Define "re.ally hot".

Keep your Mac notebook within acceptable operating temperatures - Apple Support

Any anti-virus or so-called "cleaning/tune-up" software? With the exception of MalwareBytes, those can run up the temps.

In the excellent article Bob linked, these three bullet points, after useless third-party utilities, cover the most likely suspects in overheating:

---Use your Mac notebook on a stable work surface that allows for good ventilation. Don’t use your Mac notebook in your bed, on a pillow, or under covers.

---Don’t put anything over the keyboard. 

---If your Mac notebook has ventilation openings, don't put anything into them. 

To me, "Don't put anything over the keyboard" includes not running in "clamshell" mode (lid closed while using an external monitor).

Respect both the intake and exhaust ports:

"Really" and "Extremely" hot are subjective terms. Your computer will shut down before it gets too hot. If you are concerned though, you should take your computer to an authorized service center for evaluation.