Salary increment

Can i have a salary increase even if i've worked on my company for only 2 1/2 months long? I've been hired as a storekeeper with a basic salary of 600 us dollars only. But now I have a lot of duties and responsibilities. I do the secretarial jobs of our department, preparing notices of arrivals with the attached documents. Im supervising 3 truck drivers, 1 forklift operator, & 8 helpers on the unloading, loading & transferring of materials. Receiving 1 ship of materials twicw a week such as Mechanical, Electrical, Plumbing, Structural, & finishing materials for the construction. I do the inventory also of the said materials. Arranging the files of the said staffs of our department.. Please help me to do a increment & promotion letter.