I am a Muslim but in my past, I have done terrible things. I have sex with multiple women, went to clubs, did drugs and drank alcohol. I have always wanted to repent and now I think I have found my calling. But, I don't know if I am still considered a Muslim after what I've done. What should I do?
In the Quran, God promises that He forgives all sins, as in the following passage which applies directly to your situation:
53. Say, “O My servants who have transgressed against themselves: do not despair of God’s mercy, for God forgives all sins. He is indeed the Forgiver, the Clement.”
54. And turn to your Lord, and submit to Him, before the retribution comes upon you. Then you will not be helped.
55. And follow the best of what was revealed to you from your Lord, before the punishment comes upon you suddenly, while you are unaware.
56. So that a soul may not say, “How sorry I am, for having neglected my duty to God, and for having been of the scoffers.”
57. Or say, “Had God guided me; I would have been of the pious.”
58. Or say, when it sees the penalty, “If only I had another chance, I would be of the virtuous.”
59. Yes indeed! My Verses did come to you, but you called them lies, turned arrogant, and were of the faithless.1
Start to read the Quran as if it was sent to you personally, as the Pakistani poet Muhammad Iqbal says his father taught him, and you will find everything you need in it.
If you renew your allegiance to God by accepting to obey His commandments from now on, then you are a Muslim. Repentance is sufficient to erase the sins of the past:
70. Except for those who repent, and believe, and do good deeds. These—God will replace their [past] bad deeds with good deeds. God is ever Forgiving and Merciful.
71. Whoever repents and acts righteously—has inclined towards God with repentance.
72. And those who do not bear false witness; and when they come across indecencies, they pass by with dignity.
73. And those who, when reminded of the revelations of their Lord, do not fall before them deaf and blind.
74. And those who say, “Our Lord, grant us delight in our spouses and our children, and make us a good example for the righteous.”2
Also see:
How to repent from zina (sex outside of marriage)