Beta hcg results

I want to do a beta hcg test 29 days (50th day of cycle) after having sex, do you think the results will be reliable after this time? I have irregular cycles (35-50 days) and I'm kinda not sure if I had a period this month - there is brown discharge with clots that lasts like 8 days now (there was a bit of blood a few times), I was extremely stressed for the last few weeks. I did a home test yesterday and it was negative. After what time is beta hcg reliable?