Could I be pregnant?

In January I had a miscarriage at 4weeks, I believe its considered a chemical pregnancy. After this I went back on birth control, nexplanon implant. The first month I had no side effects but then I started spotting. The spotting has been on and off for about a month now. Today I noticed some lactation, not a lot just a little when I apply pressure.

My question is, is there anyway I could be pregnant still? I haven't lactated since my son was a month old, he's now 2. I've taken all kinds of pregnancy tests and they've all been negative. Advice? Ideas?

TIA