Entex symptoms and conditions

my 10 year old daughter was put on singulair by an infectious disease doctor that had seen some improvements in kids taking this who have chronic sinus infections and swelling of sinus tissues...my daughter showed an improvement in sinus problems but noticed a 20 pound weight gain from 62 to 82 pounds in a few months..owed this to better health from pill and tonsil/sinus surgery...went off singulaire that summer...at Christmas my daughter caught a bad cold which turned into a potentially fatal frontal sinus infection from infected swelling frontal sinus (called Pott's Puffy Tumor)...she was put on IV antibiotics and singulair..she takes nasonex and sudafed regularly and does daily sinus rinsing...since starting the singulair again she is increasingly hungry and she is gaining weight again...slightly moody, never feels full...but the new symptom is pain in her side at the lower rib cage..this started after singulair for 2 months...the pain wraps around her side and reaches to her navel area...last night she woke up with severe cramping in her stomach every 10 minutes like labor contractions....after an hour she developed all over hives and was having hot flashes during the cramping...she had just taken her second dose of Entex which is an expectorant to thin her sinus mucous...at the time of these symptoms she has been off her IV drugs for 3 weeks...so these other posts really make me suspect singulair for weight gain and abdominal/rib pain and cramping..anyone with similar symptoms?..