What Are The Chances Of Pregnancy Through Non Penetrative Sex?

I am starting to get concerned. 6 and a half weeks ago now I was in sexual contact with my boyfriend. We were both naked and he was rubbing his penis against my vagina, but there was no penetration. This was two days before my period was due. Two days after this my period came, so right on time. It was completely normal, lasting around 5 days and a normal flow. I was not in any sexual contact the next month. 28 days after the period just mentioned, my next period came. However, unlike my normal period I had a light brown discharge instead. This lasted five days. On one evening I went to the bathroom and there was normal blood, but this cleared and the brown discharge continued. There was normal blood again one morning, and again it cleared and the discharge continued for another day or so. I started to get concerned cause I read that this sort of period could actually be implantation bleeding. After this period finished I had a persistent pelvic and lower back ache which furthered my pregnancy concerns. This pain has lasted about a week and a half and now seems to have eased. I took a urine pregnancy test a week and a half after this period started and it was negative. However I am still concerned. Yesterday (which would be almost 2 weeks since the odd period), my breasts became quite tingly. This has continued today. My main concern is the possibility of pregnancy, and if not, what else could be up. Any advice is much appreciated