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Have any of the doctors you've seen prescribed you anything for nausea? There are also some other (legal) and natural things you can try to help with nausea if you don't have prescription medication. For example, ginger, a natural root, can be made into tea or found in candies and this has well-documented anti-nausea properties. There are also some acupressure points located on your inner wrists-- about 3 fingers up from the crease-- that, when pushed on, can help relieve nausea.
Other than using these short-term fixes, I would have to agree with your doctors that it makes sense that your throwing up could be stress related and that dealing with your stress could provide the longer-term relief you're seeking. Talking to a therapist about your stress and grief over losing your dad could really help and I would recommend this.
Also, while smoking pot might temporarily help with your nausea, pot can frequently increase anxiety symptoms and numb feelings- both of which would ultimately make things worse for you in the long term.