Yes, that is very normal.
Many people think grief is a one time event, or maybe an event that lasts a year or two, but in reality, grief is a lifetime event. The sharp pain of loss goes away over time, but missing someone who was very important to you never stops. It's especially common when you have a milestone in life, like graduating college, or starting a new job, or turning 30, or getting married - things you would have shared with her, and she's not there.
If you find yourself crying all the time, or unable to participate in and enjoy normal activities because of your grief, that would be the time to get help, but it sounds like for now it is just missing someone you loved, and that means she was very important to you and it's normal to miss her.