Hi there, I have understood your concern and I will suggest you the best possible treatment options.
First of all do not panic.
It is unusual but not uncommon to forget the tampon in the vagina.
Stinking smell is due to growth of various microbes.It might cause infection and inflammation to pelvic organs.
It is good to know that you have already Removed it from vagina.
The tampon might have worked as a barrier
contraceptive and would have not allowed sperms to go ahead in
uterus. So I will suggest you to wait for your expected date of menses. If you happen to cross your dates then please get morning's first sample of urine tested for
pregnancy.
Also, seek prescription support from your treating doctor for a broad spectrum antibiotic like Doxycycline 2 times a day for 5 to 7 days and vaginal suppositories containing
Clotrimazole and
Clindamycin for a week.
I hope this answer helps you.
Thanks
Dr. Purushottam Neurgaonkar