It seems from your question that the stitches are not self-dissolving. (If the stitches are self-dissolving, you may rely on the opinion of many halachic authorities, which our site follows, that self-dissolving stitches are not a chatzitzah and a woman with them is permitted to immerse as usual.)
Assuming the stitches are not self-dissolving, we need more information to assess your case: Are the stitches raised above the skin? Are they loose enough for water to penetrate easily? How long will they be in place after your scheduled immersion? If you do not immerse on your planned mikveh night, will you make it to the mikveh before your next menstruation? Are there any other factors of which we should be aware (e.g. marital difficulties, fertility challenges, etc.)?
Refuah sheleimah!