Breastfeeding & Periods

Hi all, I've just had my 3rd baby but this is the first time breastfeeding, he is 12 weeks old and I ended up getting a period. Seemed normal enough lasted a week and was very heavy which I expected.. It lightened up and ended but now I've been spotting on & off. Firstly is this normal - and I'll also add that I have never totally breastfed, he's always been "topped up" with formula which I know would decrease my milk. He still jumps on a few times a day for short times but mainly at 3-4am.. I'm just wondering if this bleeding on a off (when I wipe after a wee) is normal. TIA xx