Need some advice

Sally • TTC for baby #2
Ok girls I need some advice. 
I was given a HCG shot 11 days and go and had an IUI 9 days ago. I'm 9 dpo and took a test today. There is a faint line but I'm thinking it could be residual HCG in my body. However when I just went to the bathroom I noticed a small line of light brown discharge. My questions are...
1. Could the HCG still be in my system? 
2. Could I get a positive test from the HCG and start my period. 
3. Or could I be experiencing implantation bleeding? 
Sorry for all the questions. Just need some feedback.