Please go back to your doctor or head to A&E now, especially with the yellow vomit, this one better not wait. Vomiting that colour can mean your body needs fluids and checking, and the tablets not working is also something they need to know about right away. I know it's scary and stressful, but your body and baby need proper support now. Once the doctor sees you and gets things under control, you'll feel so much better and can focus on nutrition again. Hang in there, and please don't delay on this one.
I've been in your situation before, maybe u can try eating really small portion each time. for my first trimester I depended on fruits and crackers to help me get by. please make sure that you are still drinking enough water as if you are dehydrated and have bad morning sickness, you might need to go hospital and get IV drip as there is a possibility of getting HG.