Question: Need help!

just had a baby 4 months ago. I have regular cycles even after having him. I usually go 7 days heavy. July 20th I had spotting for 3 days, took test negative. But after the test sits for a bit there’s a faint line. I started having brown spotting August 24th late at night, the next day it was light pink, the 3rd day turn red and a little heavier and after that it got light pink and brown again. My stomach is hard above my incision, been peeing a lot and craving stuff and feeling nauseous. I just took a test and it was negative. Could I still be pregnant? When should I test?