I have droopy jowl like bulge after botox in the lower face. Why did this happen?

In order to see if this was caused by the Botox injections we would need to compare your before and after photos. If it was related to the Botox the most common reasons something like this would happen was if the wrong muscle was injected, too much Botox was injected, or the Botox migrated. Also, the DLI is rarely injected with Botox. What was the indication for this injection? In regards to the DAO, if you cannot feel the enlarged muscle then you should not be injecting it. These areas require a high degree of skill and knowledge of the anatomy in the area. These are not areas that I would have an RN or PA inject. On the bright side, if it is due to the Botox the effects are temporary and should wear off in 3-4 months. Best of luck.

In order to make an accurate comment a before and after photo would need to be assessed. Land marking the DAO is important when injecting. If you intend on returning to the same injector it is a good idea to schedule a follow up appointment to discuss your results to avoid this in the future. 

True DLI injection would change your smile and the ability to fully chew or move your lower lip.  I am unsure the injections caused this, but if there was migration of the toxin it is possible other muscles were effected.  Seeing your full smile and resting positions would help.  I suggest speaking to your injecting physician.  Avoid DLI injection in the future, DAO is okay if needed and small doses in the right location.  Best, Dr. Emer.

These areas are very injector dependent! Thus not using an expert MD injector was the issue. Now the good news the result will wear off over the next 3 months... 

It's hard to say without seeing your preoperative photos.  If you decide to botox the mentalis or depressors you have to do it at a distal attachment point, meaning away from the lip and closer to the chin.  unless you are performing this for facial paralysis which it doesn't look like you are.  

I would never inject the DLI purposefully unless I was doing it unilaterally to correct an asymmetry, like for Bells Palsy. The problem you are showing is hard to see.  No experience in this situation but perhaps injecting DAO will help. Has does your smile look now. If truly the DLI were injected, you should have an abnormal smile with difficulty showing lower teeth.