shed some light on my period!!!

so I came on on Saturday 4 days late (honestly thought I was pregnant as was having all the same symptoms I did when pregnant with my son) 1st day was really light so I thought maybe spotting. day two and 3 was light to medium and today day 4 nothing what so ever.

from the day I should have started i was getting sever cramps all the way up till yesterday . yesterday mid day I had a lot of pain (keep gettib pain when I need a wee) went to the toilet and I peed out bright red blood. yet any other time when I'm on my wee is normal colour or abit darker. I am so confused.

my period is normally every 28 days and last about 7 days yet last month it lasted 9 days but wasn't heavy was really light and this month I was 4 days late and only lasted 3 days and half of that 3 days it was really light again (normally medium to heavy)

i took a test 5 days ago it was negative . any idea what's going on