Based on the information you provided the Government's citizenship checking site is actually quite helpful (it's sometimes not so helpful if you were born before 1983, but in your case it's actually okay):
When were you born?
On or after 1 January 1983
As you were born in 1992
Were you born in the UK or a qualifying territory?
No
No, the USA is not one of the qualifying territorities
Was one or both of your parents a British citizen 'not by descent'?
Yes
Yes, your mother was born and raised in the UK, and is therefore a British citizen not by descent.
Based on this you are already a British citizen by descent, meaning you have gained the citizenship from one of your parents. This type of citizenship is usually a bit limited, as in most cases you won't be able to pass your British citizenship onto your children.
See my other answermy other answer on how to apply for your first British passport from abroad.
