DOLE has representatives that can aid you in determining how to compute the 13th month pay. Remember, 13th month pay cannot be waived, unless the employer gives a higher amount than what is prescribed in the Labor Code.
If there are employment contracts, keep them and show it to the DOLE rep so that they can determine what type of employment you have with your employer. It will also serve as evidence regarding the existence of an employee-employer relationship, which is crucial in any labor-related case.
Sick leaves and vacation leaves, however, are dependent on the employer if he will provide his employees with such. There is nothing in the Labor Code that requires an employer to provide such leaves for his employees. Alternatively, you may ask the DOLE rep if there are other leaves under the Labor Code that you are entitled to have, like Service Incentive Leave and such.
Good luck in your current situation.