18st10 for three half weeks

Just as the subject line says, the scale has been permanently showing 18.10 for three weeks now. (Lost 10lbs since starting) I take my jab on Sunday night and experience the worse symptoms (eggy burps, eggysfarts, getting sick from both ends, bloating) 24-48hours of hell for two days then im fine again for the rest of the week. I drink 2-3lits of water a day, can barely stomach food, when I do its small nibbles of toast, salami, cheese etc small snacks, cannot eat a full meal. I exercise 3times a week, i just dont know what else to do?! Im scared to increase incase after jab is worse then now, any tips?