I dont have work contract since I come in qatar.I...

If you want to change the company that you work for, and you have not signed any contracts, find the following information:
It is not possible in any way to violate the purpose of your entry in Qatar.
If the purpose of entering Qatar is work for a specific sponsor (Employer), then you cannot work for another company. You can ONLY work after obtaining NOC from the current sponsor in addition to an approval from the Ministry of Labor to transfer the sponsorship.
Articles of law regulating the entry and exit of expatriates in and out of Qatar and their residence status as well:
Article 8
Every expatriate residing in the country for any purpose must obtain a license for his / her residence from the competent authority.
The applicant shall undertake to perform the licensing and renewal procedures within a period of ninety days from the date of its expiry.
The business owner / Employer shall hand over the expatriate's passport or travel document after finishing work or renewing the license, unless the expatriate requires the employer in writing to keep him / her at work, provided that he / she has to hand it over to him upon request.
Article 9
The competent authority shall issue a residence permit to the expatriate in accordance with the provisions of this law, and his / her name, photo, signature and a copy of the ID shall be printed on the residence and determined by a decision by the Minister.
Article 16
An expatriate who has been authorized to enter or reside for a specific purpose, or to work for a specific entity / company, must not violate the purpose for which he / she was authorized to practice, OR to leave work with the employer, or to work for an agency that he / she is not allowed to do so.
It is not inconsistent with the purpose of the residence permit for the expatriate to practice, even with the approval of the competent authority, some of the businesses in the company which he / she is a partner or authorized to sign for it.