I have chosen to switch from studying medical to social sciences as I like the latter. My mom was not satisfied with my decision and did Istakhara that indicated I should take medical. Should I follow the Istikhara despite not liking that subject?
If you already made the decision, there is no point to taking istikhara.
Anyway, it is good to talk with your mother about her concerns since she probably has some solid reasons for her view.
However, if you really don't like medicine, there is no purpose in studying it, because we don't do well at things we don't like. Also, no one wants to go to a doctor, nurse, surgeon, pharmacist, etc, who is not 100% committed to their job.
Wishing you the best, whatever you do! (And this answer is probably late!)