Suggest Medication For Inappropriate Sinus Tachycardia

I am a 31 year old female. I have a history of inappropriate sinus tachycardia since I was in high school. I took Toprol XL 25 mg for quite a few years to control it and it worked 100%. I got off of the medication about 3 years ago so that my husband and I could have a baby. I had no problems at all and none through out my pregnancy. I had my baby 7 months ago in which I had to have a c-section. Then 6 weeks later I had to have my gallbladder removed due to painful gallstones. Within days after giving birth my heart started racing again so my doctor put me back on the Toprol. It was controlled for several months. I went to see a cardiologist so I could continue to get my medicine refilled. He did an EKG, ultrasound, stress test and I ve been wearing an event monitor for almost two weeks now. All tests have been normal. I m taking 25mg of Toprol XL again but it doesn t seem to have it under control 100% like it used to. My symptoms are worse in the morning, right after I get out of bed and while I m showering and getting ready for work. It feels like my hear is beating fast and hard. My heart rate is usually 100-120, sometimes reaching 130 or so. Sometimes I notice my heart beating faster after meals too. I m unsure why the Toprol has kept it completely under control until now. I have minor stomach issues after my gallbladder removal but nothing serious (occasional diarrhea, bloating after I eat, etc.). Could the c-section or the gallbladder removal surgeries be related to my fast heart rate? Could it be anxiety? Why would this happen mostly in the morning?