Hello, I Get Birth To My Son On 24th April

hello, i get birth to my son on 24th april 2015, my period came back as early as 3 months after delivery. from 15th september then it didnt come till 23rd october which means it was a week late, then 23rd november and unexpectedly it came back after 2weeks on 8th december 2015, then 12th january 2016 which was a week late again. i am not planning and i'm having withdrawal sex after every 3days, i am having all the pregnancy symptoms and my belly is becoming big. i tried home pregnancy tests but were all negative but the last test was like a faint line. i am still breastfeeding my baby. i dont know if those changes has to be with breastfeeding or am i pregnant? i really need to know