Why Periods Are Delayed But Having On And Off Brown Spotting?

Hi I am 30 years old, married last year, no children. I also don t take any contraceptive pills. My periods have been delayed by 5 days, though I have been getting light, sometimes brown spotting on and off all through these 5 days. It feels just like I do when I m about to get my periods - bloating, discomfort, don t feel like doing much, but no flow. Something similar happened last month as well - after 2 weeks of, on and off spotting I got my periods but low at first, heavy in the middle and then trailed off with spotting. Before this my periods have always been normal - PMS symptoms, heavy flow first 2 days, and then reduced flow over the next 4-5 days. I have Thyroid and have been taking Thyrox 100 for sometime now. Got it tested recently and it is within range. Ultrasound showed nothing - regular sized fibroid is there which the doctor said is normal. I d been having some kind of itching for a while now (alsmost a year), and was recently prescribed Teczine 5 mg. I took it for 4 days, but it didn t suit me so I shifted to Allegra. I don t know why this change in my periods has happened. I had a fibroid removal surgery in 2012, even after that my periods were normal. Please help!