IUI and implantation bleeding ?

Hi ladies ,

My husband and I went in for our (lord knows what number now) IUI. My period isn’t due until the 4th or 5th depending on when the trigger shot wears off… but today I had some severe cramping and then about 5 hours later really bad lower back pain… now I’m having some light pink / red spotting … how common has implantation bleeding been for any of you ladies during cycles ? Just curious because the one time we did conceive and had a MC I had no cramping and not implantation symptoms.

Thank you in advance for any words of wisdom and sharing your own experiences.