Hey, first of all, good that you didn't stop medications because of side effects, instead you asked. And initially, when we start medications, the body takes time to adjust to meds, that's why the effects on sleep and gastric upset.
And yes multivitamins are completely safe to take with paroxetine.
Next Steps
Do not worry, wait for 2 weeks for meds to work and side effects to come down. If still, you don't feel okay please consult your psychiatrist once or take second opinion