Knit, I don't know how long you volunteered for but I can tell you it has taken me a solid month to get used to working 4 hours every other day after 3 years of being out of the work force. For 2.5 weeks I was absolutely exhausted and highly stressed. This week the fatigued an anxiety were noticeably better. I seriously underestimated the physical, mental and emotional stress of just working 12 hours a week. Be gentle on yourself and maybe ease into it slower if you elect to try again.