Is this bfp? So confused?

I have been feeling 'not right' for about a week now, having headaches, tired, nausea throughout the day, diahorrea, heartburn, low back pain, dizzy spells and just different. My periods are irregular due to stopping depo 7 months ago. Well anyway I took a first response test today as I kind of worked it out that my period would be due 7th March if it was the same amount of days in between the last af. The result looked negative but if pointed to the sunlight it does have a very very faint line or are my eyes wanting to see to see it so much am i seeing things. I have a doctors appointment on Thursday as my doctor is wanting to do blood tests to check everything ok as i have irregular periods. Any advice would be appreciated. Many Thanks in advance xx