You are 19 yrs old and your period is 45 days late from last.
If your period was regular in past then need not to be much worried.
Otherwise you may suffer from OLIGOMENORRHOEA and need to investigate properly.
It is defined as infrequent period and delay of several months in between and more common in pubertal girls.It is mostly due to inadequate maturation of H-P-O axis and inadequate hormonal
The cycle are often anovulatory in first 1-2 yrs.Gradually full development of normal ovulatory cycle and it will not have any harmful effect in future fertility
Other causes keep in mind:
1)Mental & physical stress
like vigorous exercise
nervosa-if wt less than 47kg,mens remain scanty.
4)PCOD with over wt.
So you need to do a USG,Thyroid function test,FSH/LH and prolactin
level if period is irregular or delaying more and consult to your gynaecologist.
Along with maintain a healthy diet,control wt and regular light exercise.
All the best.