What Causes Vaginal Spotting And Brown Vaginal Discharge?

Hi ! Me and my bf got intimate on 22 april last month.there was no penetration neither he did ejaculate near my vagina, precom might have come in contact on outer side while touching. I was due to have my periods on 24 april but it did not come. My menstural cycle is irregular since teenage. So i was worried if might get pregnant because i had heard people say that it might happen. I took hpt on 12 may and 19 may and 20 may both came out negative. I also took duphaston as it was prescribed earlier by doctor for my periods. I got normal menstural bleeding on 23 may and was relieved. Then it continued for next day. After that i experienced two days of spotting. This bleeding started with brown discharge and then changed into bright red. I am afraid that can it be implantation bleeding? It happened 1 month after we were intimate, or it was alight period.