psychology is not a medical stream clinical psychology although can be pursued after doing psychiatry but psychology itself is a general stream in which you pursue bachelor, masters and then Dr degrees from different universities
however if you pursue MBBS by giving neet, AIIMS and jipmer entrance examinations you have to become an MD in psychiatry after which you can practice as a psychiatrist

Hello Narayanam,
Yes, you can become MBBS after 12th. For that you have to clear entrance exam like NEET UG, AIIMS, BDS, BAMS, etc.
For more info click the link and read full article
https://www.google.com/amp/s/medicine.careers360.com/articles/medical-courses-after-12th/amp
Good luck.