I had unprotected sex three weeks ago a day after I got off my period and now I'm spotting and its dark brown and sometimes I have nothing there... and I was supossed to start my period today I'm freaking out and I don't know what to do please help

You had unprotected sex, so of course there's a chance. Go and see your doctor.

Or just take a test hun

You really don't do anything at this point, worry will not help, you made choices so I assumed having a baby was considered since no protection was used.

If after about a week late for your period, you take a pregnancy test. Use the first urine of the morning.
If pregnant, you see your doctor and let the man know he will become a dad.

Yes, there may be a slight unlikely chance you aren't. But most likely you are . You should consult your doctor or take a pregnancy test .

Yeah a baby is not planned at all.. but I still haven't started my period yet its just that brown blood or whatever that is

I meant we don't plan on having a baby