Please help Ectopic pregnancy used methotrexate hcgs weird...

I was diagnosed on the 10th with ectopic pregnancy got the methotrexate (not sure of spelling) I went for follow up blood work 5 days later my hcg levels were originally in the 800s then after 5 days they were in low 200s here a week and a half after follow up test went back again and levels are at 2... I don't understand why levels dropped so fast in the first 5 days and its taking over a week for me to drop to zero... I have had sex with my SO since my symptoms stopped which was sometime last week could my hcgs just being going down slowly now or could I be pregnant again?