you can re-apply for visit visa 3 months after exiting qatar. your visit visa after 6 months can be extended maximum to 7.5 months like what i did to my son but you have to apply for visa extension ( there is a form you have to fill up)by submiting the visa extension form in building no. 1 second floor. first extension is 1 month then re-apply again with same procedure and the will give you another 15 days.