Ay, spotting after ligation is actually pretty common, especially if your last period was heavy, sometimes the uterus takes a few cycles to settle down, kaya don't panic muna, bes! One of my mum friends also had irregular bleeding for like three months after her procedure, pero nag-normalize lang eventually, so fingers crossed the same happens sa'yo. But honestly, since you already took a PT and it's negative, I'd still suggest getting checked with your OB kasi peace of mind lang talaga, lalo na kung hindi ka rin sigurado kung normal lang ito or may something else going on, they can do a quick ultrasound if needed, and it's worth it para ma-rule out any concerns.