How can I access my medical records to show that I was in combat and to fix my DD-214?

LCpl Nicholas Wilcox did you file a VA claim already? If so they have your medical records on line at eBenefits.

If not, submit a request through NPRC. https://www.archives.gov/veterans/military-service-records

If you have not been out very long they may still be at your last military treatment facility. Contact Patient Records.

You file a request for correction and they issue you a DD215 that's basically a correction to the 214, https://www.archives.gov/veterans/military-service-records/correct-service-records.html

LCpl Nicholas Wilcox are you in contact with anyone else you were deployed with? They could write sworn statements attesting to you being there. Do you have an award from the deployment on your 214? Doesn't have to be a DSC. The GWOTEM? CAR? ICM? PH?

Do you have a pink copy (Service Member) of the post deployment health assessment that they were doing back then? You would have done it at the APOD on the way out of theater. It also would have your deployment dates on the top.

What documents do you have? Did your unit cut orders for deployments? People would have needed these to store vehicles and break leases. The Army issued orders and the References the manifests for flights. Do you have any LESs from that time showing you drawing hostile fire pay etc? You can order them fromDFAS.