What Causes Vaginal Spotting During Early Pregnancy While On Clexane?

Hi I am on clexane 20mg and I am 6/40 gestation I have had previous misscarriges and have been on clexane now for around 4 weeks and for the last few days I have had spotting but not enough to go onto a pad and I am wondering should I be worried and is it normal to spot in early pregnancy with clexane injections