Why am I getting a positive on one test and negative on another?

I had a miscarriage on the 11th of October. Yesterday I took a test using early response and it was positive. However, a friend told me that I can possibly still have HGC in me from the miscarriage. Today I used clear blue and it said negative. I went back and tried again with early response maybe an hour later and it is showing positive again. I'm confused.

Has anyone been in a similar situation? If so, can you explain what is happening.

Why am I getting a positive on one test and negative on another?
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