can implantation bleeding be somewhat heavy?

Marisa
So for the past 3 days I've been spotting and then it goes away and turns into light pink to brown discharge like when I finish my period . The first day I thought my period was starting so I put a pad on and nothing when on it the rest of the day. 
Before bed I wiped and there was absolutely nothing so I took the pad off and  went to bed . In the morning I went pee and my underwear were stained with 3 dark Nickle sized  dark red blood marks . I put a pad on again and wore it al day. I had tiny brown discharge. Same thing in day 3. I am now 15 dpo and according to glow my period should have started 2days ago. 
I will test later today but... Have any of you experienced this as implantation bleeding ?