Throwing up after eating

We just recently started introducing 1st solids- just cereal mixed with breastmilk. The first time, she was up vomiting all night so I took her to urgent care the next morning and the doctor said it sounded like just a sensitive tummy since she was really mucusy. To come back if it got worse but otherwise don't worry about it. So we of course waited until we were all better and tonight we tried introducing solids again. She projectile vomited everything in her stomach. So we gave her a bath, waited a little bit, then I nursed her and went to lay her down for the night, she threw up her whole feeding. I'm nursing her again now, I'm making her a doctor's appointment for this week, and we're just going to wait a few more weeks before trying solids again. But does anyone else have any insight? She's been exclusively breastfed since day 1, no reflux issues, she doesn't even spit up very much. Dad nor I really have any food intolerances and we're all healthy so no colds or anything else to suggest a stomach bug like last time. Ideas? Experiences?