thank you for your query.
It is not normal to have a lot of pain and swollen vaginal walls after IUD insertion.
You should consult your gynecologist to rule out the possibility of a pelvic infection
which is seen sometimes with the IUD.
Also, you should not have any trouble feeling the IUD strings.
It is possible that the IUD might have been expelled with your period.
Also, the IUD might have migrated upwards leading to inability to feel the strings.
Please consult your doctor, as an infection, if untreated , can lead to complications.