Spotting and negative hpt

Ok, my husband and I have been ttc. I had a miscarriage/d&c in may. I was 11wks and baby had passed away at 8 wks. My period came 45 days after on June 30. We got the go ahead from my dr to start trying again. I used opk to see if and when I was ovulating. According to those I did on day 16 of my cycle. I also spotted on day 14. Then I spotted 12 days past ovulation and again on 15 dpo, only on 15dpo I thought it was my period at first because it was bright red blood. But that happened in the morning when I wiped. Later when I wiped it was brown. Then nothing. It is now 16 dpo and day 31 of my cycle. I took a test today and I though I saw a faint line, but it could have been my eyes playing tricks on me. On day 14 dpo I tested and it was negative. I have been feeling really weird, with cramps but not any pain, and super nauseous today. What do you think could be going on?