Early spotting and now back pain but neg test

Hi, I am on the pill and have been for a number of years. 2 weeks ago on Wednesday I missed a pill. I took my next pill as normal and carried on - I am now on my 7 pill free days. Foolishly I let my boyfriend use the "pull out method" last week, I was a little worried that I might be pregnant from that so I took a pregnancy test last week which was negative.

I now have spotting that is a pinkish brown colour and lower back pain along with slight feelings of nausea and headaches. Also for the last few nights I have been getting hot then cold. I usually feel a bit hotter when my period is due, but I don't know if any of these other symptoms are unusual or a cause for concern.

My period is due this week but other than this VERY slight spotting I haven't seen any signs of my period. I think I may have taken the pregnancy test a bit too early as I think you have to take it on the day or after your period is due otherwise it won't work so I will do another test later on in the week. But does anyone have any advice for me or know what might be causing me to have these symptoms? Any help would be greatly appreciated, thanks.