Why I am not having my regular mensuration after birth?

i have given birth at September and after that I had a regular period and I didn't have my next mensuration. I have tested my urine twice and it gave me a negative result. so now I am worried whether I am pregnant or not?

Its the lactational amenorrhoea which is occuring to you,this one the natural ways of contraception,requiring no other drugs.here there is absence of normal menstrual cycle and may prolong beyond six months.so chance of getting pregnant is very rare during period of lactation.