What should I do after repeating the Istikhara prayer three times, and not feeling at ease? And should I rely on feeling?

Psychological comfort is not the basis for Istikhara (seeking guidance from Allah); rather, it is based on whether the matter for which Istikhara was performed comes to fruition or not. So, if you inquire about this young man among trustworthy individuals and they praise him well, then accept his proposal and agree to marry him. Whether the marriage takes place or not, there is good in both; for the essence of Istikhara is to entrust the matter to Allah the Almighty, so that He may choose what is best for His servant. A Muslim woman must not accept a husband who lacks piety and good character, in accordance with the Prophet's (peace and blessings be upon him) saying: "If someone whose religion and character you approve comes to propose to you, then marry him. If you do not do so, there will be fitna (strife) on earth and widespread corruption." Hasan (definition) al-Basri said: "Marry her to a man who fears Allah, for if he loves her, he will honor her, and if he dislikes her, he will not wrong her."