three months with iud

hey ladies! i have had my iud for a little over three and a half months and i haven’t had my period in almost 100 days. i think this is totally normal but i’ve been experiencing things like really sore breasts and minor cramps. today i had dark discharge and light bleeding with slight discomfort every so often when going to the restroom but usually is fine after drinking a lot of water. i have no idea if this is just a uti. it can’t be a std because i just went to the doctor and got checked for them and they came back negative. I really doubt it is pregnancy just because i haven’t let my partner cum in me or anywhere close to that down there area. so just asking if anyone knows what this is or if it’s my body just still adjusting to the iud thank you :)