Hello I Have Been On Depo For Six Months But

Hello I have been on depo for six months but had an instinct I might be pregnant I took a Lloyds pharmacy early test on Wednesday morning and it came back positive very faint but it was there , I took the 2nd test yesterday morning and the line came straight up as clear as day positive, so I brought a first response test and did it this morning and it is negative ? What can this mean ?
Thank you Kirsty.