Is this normal to have no period, after having a couple of them after giving birth?

I'm 18 with a 7 1/2 month old baby boy, i had a couple periods there but my last one was almost 3 months ago about may 10th,i feed so i don't know if that has anything to do with it.i've been having cold flashes, it can be slightly painfull during .i have nausea, lack of appetite,the cramps are extremely painfull which can be normal for me but only in the middle of my period.i have gone in to the near by planned parenthood to do a preg-test it came out neg twice. i plan on going in tomarrow, for another one.but its uncomfortable i have been in there 2 times in the past 4 months and they treat me like i'm irresponsible when i tell them my boyfriend/babys daddy and i don't use a condom, or birth control. its non pleasurable and i have tried a couple birth control and it only makes me feel like ****.[sorry for my language.]i plan on gettin on one soon.