Hello and welcome to HCM,
I do understand your problem regarding the swelling in the neck. You should understand that unprotected sex involves some amount of non hygienic contact and thats the main cause of infection after the same.
This may be the same with you. You might have either strained on performing the act or got an infection which could have infected your throat .
For all these I would normally recommend an antibiotic like the amoxycilln- clavulanate
625 mg twice daily after food for five days along with tablet pantoprzaole 40 mg twice daily before food for two weeks. Your doctor will know about these.
Meanwhile take lots of warm fluids and do not strain further.
Wait for a week or two after you take the above treatment for the symptoms to go away. If they persist then take a throat swab, upper GI endoscopy
and get back to me with the reports
take care and be safe
Dr Sriram Nathan