1. Could I be pregnant while only on one depo shot? 2. When is best to test again?

[Polkadotqueen]

I have three questions.. I got the depo shot December 21st 2016 and I am supposed to go for my second one March 20th 2017 (today) I get my period 21st of each month) But I has unprotected sex with my boyfriend about two weeks ago (March 3rd) and he ejaculated in me twice within that day and about a week after I noticed I've been getting white discharge on my underwear for about two days then after I spotted for a few more days along with random nose bleeding and wakin up in the night to my  saliva all over my pillow, my stomach is bloated and cramping, I've already been having the dizziness and headaches but I've noticed it being worse. Also using the restroom more frequently. My nipples have swelled up all puffy like and I noticed a line going down from my belly button. I took a home pregnancy test on the 17th of March (about 4 days before my period) It came out negative but is it possible I tested too early? Could I be pregnant because I am only on one shot ? When is the best time to test again ?