I apologize for the length...

Good morning ladies. I desperately need your advice. I am a mom of a 19 month old, miscarried at the end of March, and am now facing another possible miscarriage. I received my BFP on July 7th, and was taken to the emergency room on July 10th for severe cramping. My HCG was tested and determined to be 101. No sac was located. They did an MRI and saw nothing in my tubes. I met with my OB on July 12th. HCG was retested and was determined to be 100. Due to a lack of increase, my OB deemed my pregnancy to be non viable. HCG was tested again that following Monday, July 16th and was determined to be 172. Levels barely increased. My OB suggested a methotrexate shot in order to avoid possible surgery. My methotrexate shot was given July 17th and HCG was tested again July 21st. HCG levels have raised to 342. Is this normal? Has anyone ever had levels raise? I am still not bleeding and they are mentioning another shot. Is this a sign my pregnancy is going to last, or should I follow through with suggested treatment? Any advice would be amazing! Thank you in advance!!