Scripture is always a good place to start to seek encouragement and strength when fasting.
Remember all the sufferings that you had to meet after you received the light, in earlier days: sometimes by being yourselves publicly exposed to insults and violence, and sometimes as associates of others who were treated in the same way. For you not only shared in the sufferings of those who were in prison, but you happily accepted being stripped of your belongings, knowing that you owned something that was better and lasting. Be as confident now, then since the reward is so great, You will need endurance to do God’s will and gain what he has promised. Hebrews 10 : 32-36