"Does the first amendment mean we can discriminate?"
It means government can't discriminate, government can't favor one religion over another, government can't seek to preempt religious expression, and government can't seek to codify religious dogma in secular law.
Private citizens are at liberty to discriminate, provided one understands there are consequences for doing so in the context of private society, and in a free and democratic society.
Private businesses open to the general public aren't allowed to discriminate in jurisdictions with public accommodations laws that provide protections to certain classes of persons.
Laws prohibiting discrimination are Constitutional because their intent is regulatory, not to disadvantage religious expression or free speech – one may not claim a 'religious exemption' as an 'excuse' to violate an otherwise just and proper law, such as public accommodations laws.
Private citizens can't 'violate' the First Amendment rights of other private citizens; for private citizens to call for a boycott, for example, of a private individual or corporation that engages in discrimination doesn't 'violate' the right to free speech of either the individual or corporation. Only government has the authority engage in prior restraint or preempt free speech, where First Amendment jurisprudence determines whether such government action complies with the Constitution, and measures repugnant to the Constitution are invalidated by the courts.
Given the posts by conservatives in this thread, ignorance of the law, what is or isn't discrimination, and whether government has engaged in discrimination or not is as much a problem as discrimination itself.