Having Trouble Gaining Weight--- Any suggestions?

I am a married woman with two children ( 1 Biological & 1 step)... I am 5'5" or 5'6" and I have been healthy all of my life minus two times (after having my daughter & a week ago)...

At 17 years old I stopped growing (height wise) and I weighed around 145-152 pounds. I was not fat in any shape or form. My doctor said I was one of the healthiest young adults he has ever laid eyes on. My BMI was normal, along with all vitals.

After having my daughter at 18... I experienced having a blood clot in the left lung. I also had tachycardia and high blood pressure. They put me on BP Meds, HR Meds and bloodthinners for nine consecutive months. I was released off the medication and was told I would continue being healthy.. I weighed 135 pounds at this time.

I got in a relationship when my daughter was 8 months old. It started out good and then he became an abusive partner. He told me I wasn't pretty unless I weighed under 90 pounds. And he even went as far as making me not eat. After we split, I went to the doctor to find out I weighed 78 pounds. I worked hard every day to try to gain my weight back.

I got back with my daughter's biological father and he started helping me. I was eating between 2400 and 4800 calories a day. I was trying to eat a lot but not too unhealthy... I work in an office day in and day out. I don't do any heavy lifting. I do exercise at home but not strength training or anything.

Most of my exercises are dumbbell squats, lunges, planks, jumping jacks, etc.. I even do Yoga 3 times a week. I am just becoming at my wits end with this issue. I don't know if there is something internally wrong with me or what...

Does anyone have any suggestions..