any advice?

Rachel
So I thought I got a faint bfp last Wednesday/Thursday (9/10dpo) with clear blue but then had a negative at 11dpo with a cheapy Tesco test. 
Had cramps all last week which is unusual then started spotting Saturday (12dpo) and lots of cramps. Spotting stopped this morning, which is when I should have come on my period!! 
My cycle is like clockwork and always very heavy for the first two days, lasts about 4/5 days so I am very confused! 
Should I do another test?