False positive or chemical pregnancy?

Sonia
Hi ladies, was having faint positives over a few days with FRER old style tests then started spotting brown which turned to red after a few days- much lighter than a period with very mild cramps. Went to doctor which showed negative urine and blood test HCG level was 4 which is not pregnant. Could have this been a chemical pregnancy or false positive (keep in mind these faint positives were showing for a few days testing)? The doctor couldn't explain why I had a faint line and had referred me to another doctor. Any advice or experiences would be greatly appreciated! 💜