If you check back, I too lost my mom when I was 18. She had kidney cancer that spread and was diagnosed late. I am now a 35 yr old woman with two boys aged 16 and 6.
The pain of losing your mother never goes away, it just changes. It becomes a part of you, a more bearable part that doesn't weigh so heavily as the years pass.
I was terribly angry from age 18 almost until age 30. I would go into a rage over minor things like car breaking down, someone saying something I didn't like, having extra crappy day etc. When really, I was hurting over losing my mom. It seemed to make me angry at the world for some time.
My biggest advice is get some counseling. Try out talking to someone, keep trying until you find a therapist you are comfortable with. Residual feelings from losing parent so young can negatively affect your life in ways one doesn't necessarily realize until later. ***Get your feelings out with a professional sooner rather than later. I waited too long to get counseling and I feel it affected my quality of life all throughout my twenties.***
Special situations like birthdays, graduations, going off to college, Mother's Day, Christmas, when you become a mother yourself and realize your mom won't know you as a mom or as adult can be devastating. Know you are not alone in feeling this way. Many women including myself are on this journey with you.
I recommend a great book called Motherless Daughters. Also, most Hospice locations offer grief counseling or group meetings with other young adults who've lost a parent. It helps to know you aren't alone, it helps to get tips from a professional on how to navigate life without your mom and your feelings surrounding it.
It's okay to cry and feel what you feel as it comes. Grief comes more in waves, as opposed to a linear process that only gets less over time. At times it will be exacerbated when you least expect it. Other times you will feel more at peace. Just ride out those waves, feel what you feel. It's okay.
Try to look upon yourself and love yourself as your mom would have looked upon and loved you. It is what she would want. Focus on the little pleasures in life and how much you have ahead of you, try to be present and absorb all the opportunities around you for happiness and experience.
As a mom who lost her mom, sending warm thoughts to you.