I Am Currently Taking 25 Mg Of Mirabegron Along With

I am currently taking 25 mg of mirabegron along with 30 mg of mirtazapine at h.s.for severe IC symptoms. However, I have just had my mirabegron increased to 50 mg as I haven't slept long than 2 hours straight in the past two weeks. I am concerned of the potential drug interaction with this increase. I also take 15 mg methadone at hs for central pain syndrome and 50 mg topamax for migraine prophylaxis. Thank you as I am worried about seratonin syndrome but need to sleep!