Why could i have chest pain after vomiting?

Couple of reasons: Chest pain induced by vomiting is unlikely to represent angina, though it is possible if the vomiting is an atypical presentation of heart attack. This can be seen occasionally. The esophagus can undergo significant strain during vomiting/retching, and it is even possible to tear it slightly, which can be dangerous if not immediately detected.

Vomiting: Vomiting brings up acid from the stomach, this can irritate the esophagus--- which can cause esophagitis resulting in chest pain.

Probably because...: ... your esophagus was just bathed along its entire length with stomach contents, including acid!