Isaiah 7:14 does not mention a virgin birth. The seventh Book of Isaiah has to do with King Ahaz of the Kingdom Judea. In 732 B.C.E. the House of David was facing imminent destruction by two fighting kingdoms: The Kingdom of Israel and the Kingdom of Syria. King Ahaz and the House of Israel were terrified and G-d sent Isaiah to reassure the king that he would be protected and the two armies would not succeed in destroying Jerusalem. The alleged virgin birth would not occur for another 700 years.
Read Isaiah 7:11 and 16 to get the correct context.
Isaiah's words are prophetic not limited as to what would happen to Ahaz, but as verse 11 Ahaz is told "Ask thee a sign of the LORD thy God; as it either in the depth, or in the height above."
But Ahaz answers 12 "I will not ask, neither will I tempt the LORD."
The 'sign' was given anyway. 14 Therefore the LORD Himself shall give you a sign: Behold, a virgin shall conceive, and bear a son, and shall call his name Immanuel.
Immanuel means God with us, and of course that birth did not take place for around 700 years.
15-25 is history now but prophecy to Ahaz. Just as the 'sign' was prophecy to Ahaz and history to us.