Can infection appear 4 days after birth?

Va

I was in the hospital for 3 days, on the third day we were sent home. I was feeling great, my son had a fever for 2 days, but couldn't find the reason why... The next day I started having fever, the day after I was feeling bad upper stomach pains, every time I swallow something or even just burp it hurts so bad, but for a second. I thought I have a stomach bug, but no idea what could it be. I said to midwife cause she was here today, she basically said that I'm fine. Been feeling today very light headed as well, maybe cause I haven't slept basically in 2 days? And I'm pumping milk as well and it makes it worse every time I pump....