Weird period?

Crystal

I've been on skyla for a few months and my period is usually very long but not necessarily heavy and comes at somewhat different times of the month. Two nights ago I started bleeding but it stopped by morning and then disnt start again until last night and this morning I woke up and bleed largish clots but the bleeding stopped again. I did a string check and the strings are good but should I worry about pregnancy or my IUD?