What can I do if my dissolveable stitches are falling out after oral surgery, this normal?

Yes . The resorbable sutures start to "dissolve" because of an inflammatory reaction that occurs in the body. They are meant to start "coming loose" or dissolve in 7-14 days. Sometimes they will fall out sooner if the knot unravels so it depends on how long ago you had them placed.
Depends. There are different resorb-able sutures types, with different dissolving time frames. These time frames are also an average and depend upon several factors - including a patient's enzymatic activity. Additionally, your diet and oral "activity" could also cause the premature loss of sutures. Within a few days of surgery, then no it is not normal. Give your oral and maxillofacial surgeon a call.
Yes. The dissolvable sutures should fall out in 3-5 days.