Am I an asexual? I lack sexual attraction but not sexual drive.

You could be! Lacking the attraction but not the drive does not take you off the spectrum. I myself am an asexual who prefers to give than receive.

Sexuality itself is a fluid concept. Maybe you are not attracted towards a particular gender. You can explore more about whether it is not a sexual attraction towards anyone at all irrespective of any gender or it is about a particular gender. Give yourself enough time to understand about it. Think about what are your feelings about same sex people and different sex people. Maybe you feel certain things about someone but you face some difficulties to accept that. And being asexual is alright. It can be a phase of your life. You just need to understand your feelings and it will surely guide you towards your answers.

Asexuality has to do with a lack of attraction of a sexual nature. And there's nothing wrong with that or anything in the gender identity and/or sexuality spectrum

Asexuality is the lack of sexual attraction. Some asexuals still experience low sex drive and/or think about sex but have no desire to act on those feelings. Gray-asexuals usually fit into this category.

No. My understanding is that someone who is asexual lacks both sexual attraction and sexual drive that cannot be satisfied by masturbation.

You are the master of you. You know you better than anyone! So, I cannot tell you if you are asexual or not. Here's a link to a 7 cups forum on asexuality, that may assist you in figuring this out. http://www.7cups.com/forum/GetSupport_28/LGBTQMembers_60/AAWRelationshipsandAsexuality_6872/

Asexuals are not sexually attracted to someone while aromatics lack romantic attraction to someone. Of course, it differs from person to person and I would recommend not trying to find a label that suits you but rather researching further on the topic.

It depends on each person. You are the only person who can determine who you are. Take your time and figure yourself out.