HCG SERUM TEST

Hcg serum QN showed my hcg levels aren't high enough. Hcg serum QL that says neg or positive says positive. One doctor told me I'm pregnant but my hcg levels are too low right now. Period due Monday. At home test says negative as it did with my 3 year old until the day of my period and my hcg level with her were super low too and I was right at 3 weeks with her. Anyone else had this happen with the blood test tho?