What is the expiation for not attending wedding invitations due to social phobia and chronic flatulence, and is donating 100 dinars as charity for each un-attended wedding considered an expiation?

If you do not attend invited banquets due to your illness, you are excused and commit no sin, nor are you required to offer expiation, because answering an invitation is obligatory only when there is no excuse. It is advisable to consult a trusted psychiatrist regarding your illness. As for continuous flatulence, it obliges you to perform ablution for each prayer after its time has begun, and you may pray the obligatory prayer and as many supererogatory prayers as you wish with that ablution until that time expires.