Might be pregnant?

So me and my fiance are trying to have a baby on July 5 we did it and he put the sperm in and ever since everytime we do it hes put his semen inside me which we both agreed on. These days I've been expieriencing alot of lower back pain heartburn tiredness etc. My period was suppose to arrive on July 17 and it always arrives in the afternoons. My period didnt arrive and today July 19 I woke up and went to the bathroom and when I cleaned myself I wiped blood with mucus and it wasnt that much. How do I for sure know its implantation bleeding ? I'm scared maybe me or my fiance might have a problem and I'm not pregnant. Also I haven't tooken a pregnancy cause I thought it might be too early. When should I take a pregnancy test? Please Help Me