Brown discharge before period

So I'm having brown discharge and it's been going on for 4 days. My period is supposed to come tomorrow. I didn't have sex for like 4 months (last sex was on 20th October) and I'm having my period since. And it's regular. And all blood tests came negative (they've been done 3 times in December). Why is this happening ? My last period was on 29th January and brown discharge happened before that period too but didn't last this long and period came. Is it because stress? Is it an affect of dropping birth control ? (I took birth control for just one month in November and then I quit because of migraine) Btw I'm having cramps too.