IUD & no period

I had my IUD inserted in September 2017 and its April 2018 and went through irregular bleed the first 3 months and then it went back to my normal period schedule. I'd always get it around the 19th or 20th of every month. I got my period last month on time. Then this month hit. I was getting all the signs of my period; back pain, vaginal cramping, bloading, and then the hit of really bad cramps the day off my period coming. But only a drop of blood came out and never came back. So Ive been having the cramping and stuff but no period. Im concerned. I have an app with Planned Parenthood tomorrow but i would really like some idea on what it could be.