Can this be a reaction to sutures? (Photos)

It's good you are communicating with your surgeon regarding your condition.
This appears to be a hypersensitivity issue along your incisions. It can be seen with the use of steri-strips after a tummy tuck. Steri-strips are pieces of tape used to cover the incision after surgery. They are stuck on with a sticky substance. Some patients are allergic to the adhesive and break out in a rash over the site of the steri-strips. You seem to display this pattern.
The location of your rash might also be a sign of a sensitivity reaction to antibiotic ointment. Prolonged use of antibiotic ointment can keep the incision moist and keep it irritated. Some people are allergic to the sulfa in triple antibiotic ointment.
If your physician has ruled out an infection, then you can treat the hypersensitivity reaction in several ways. First, stop any topical antibiotic ointment. Keep your incision dry. Prescription steroid cream can help settle the rash. Creams dry quickly. Don't use a steroid ointment. Steroid injections and steroid dose packs can also help resolve the issue. Benadryl, especially at night, can help. If this is a hypersensitivity reaction to the steri-strips or antibiotic ointment, it could take a few weeks to resolve.
Good luck and keep in touch with your surgeon so he can guide you through this.

It appears from your photos that you have a hypersensitivity. it could be a reaction to adhesives, medications, irritating clothing, or something else. It is good that you are in close contact with your surgeon. Keep him/her aware of any changes or if you do not begin to see improvement.

You are doing the right thing by keeping in close contact with your surgeon.    The irritation seems to be localized.    Dissolvable sutures are dissolving at this time which can be irritating.   There are several other agents like tape adhesive, topical silicone, moisture,  etc.    Good luck.