IUD HELP

So I've had the iud for about 9 months now and my period has been pretty normal, just slightly off timing-wise here and there. Never had an issue. On the record I have been very stressed out lately but last month I had sex on July 5th with a condom but my period was 5 days late however once I got it, it was heavy and lasted longer than usual. Now this month I was "fetal position" stressed out with little sleep for a while, then went on a weekend vacation where I seemed to have a very light 4 day period, then it went away. This concerned me because my period had always been normal except for lately. Is it stress throwing it off?? Could I be pregnant even though I had a full period last month and have no pregnancy symptoms?? I am now spotting again, being 13 days late (if the spotting wasn't my period at the beginning of the month). I have also been on antibiotics for the past week as well. I don't know what to do or what to think. I really don't think I could be pregnant as I had sex once last month with 3 forms of protection and then I had a full heavy period. Thoughts??