All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
First of all, we ask Allaah to relieve your distress, make a way for you to get out from your difficulty and comfort your eyes.
Dear sister, first we advise you to supplicate Allaah earnestly as He answers the supplication of a person in distress and He is the One Who relieves sorrow. Allaah Says (what means): {Is He [not best] who responds to the desperate one when he calls upon Him and removes evil.}[Quran 27:62]
Also, you should mention Allaah as much as possible as by mentioning Him, the hearts get comforted. Besides, you should keep company with pious women so that they would help you and give you advice.
It is good that you are keen on being kind and dutiful to your father and endeavor to please him; this is indeed a good trait in you. Hence, we advise you to try to convince your father that you do not wish to study medicine and that you want to get married. You should clarify to him that the older you get, the lesser your chances of getting a marriage proposal will be.
Indeed, marriage is a righteous act for which a person should hasten to; rather, marriage can be an obligation for whoever fears to be tempted to commit illicit sexual acts as we clarified in Fataawa 87295 and 84026.
In fact, you live in a country where the reasons of temptation are widespread. Hence, your guardian [who is your father] is himself required to endeavor to marry you off to the suitable and competent man who asks your hand.
In any case, you should try to convince him and you may seek the help of your relatives or others whom you think may influence him. If he is convinced, then praise be to Allaah, otherwise you are not obliged to obey him in matters that cause you harm. For more benefit on the conditions of obeying the parents, please refer to Fatwa 84942.
In case a suitable and competent man proposes to marry you and your father refuses to marry you off to him, then you may take your case to one of the Islamic centers in your country.
As regards your father's spending on you from ill-gotten money, then if his entire money is unlawful, you are not permitted to benefit from it except for necessity. Studies are not a necessity that makes this permissible. In case his money is a mixture of lawful and unlawful money, then it is not forbidden to benefit from it but it is disliked.
For more benefit on the necessity which makes what is forbidden permissible, please refer to Fatwa 133818, and for more details on consuming ill-gotten money, please refer to Fatwa 87211.
Allaah Knows best.