Hello My Name Is Jessica I'm Nineteen And I Have

Hello my name is Jessica I'm nineteen and i have missed two periods now. Last one was in August and it was light. The only thing that has changed in my life is I started a new job waking up at 4:30am I'm constantly walking around. Ends at 4:30pm The job is only two days every week. What's wrong with me? I'm scared I'm not going to have my period and ending up going to the doctors for medicine i can't afford.