After the beach, your redness of the eyes must be caused by the exposure under the strong sun light. Your redness should be treated as soon as possible. Your red eyes could be released by the eye drops with anti-inflammation. You could also find the clean cloth and hot water to do the warm compress. You'd better drink more water and eat the food with vitamin C to moisture the eyes.
Well, for your situation, I have to say that your eyes may suffer from eye infection, which is caused by the allergy coming from the beach or the sea water. First, you should know that see water and sea wind contain many dirty objects. Because of that, it can be very easy for you to be infected by the allergy, for eyes are very sensitive, when you are in beach. To get rid of it, of course, you should wash your eyes with warm water and then have some ice on your eyes. In that way, it will be effective. But next time when you go to beach, just prepare some tools for your eyes.
It can be the ultraviolet rays in the sunshine that cause your red eyes. The sunshine on the beach, as we all know, is usually very strong, and if your eyes are exposed to the sun for a long time without any measures of sunscreening, such as wearing a pair of sunglasses, it would do great harm to your eyes. The ultraviolet rays can be very harmful to the eyes of human beings, leading to permanent damages in the conjunctiva, retina, cornea, crystalline lenses, and so on and so forth. And according to your description, it may be conjunctivitis in your eyes, which refers to the inflammation of the conjunctiva, usually coming along with eye itching or dry eyes. You can try using some eye drops such as sodium cromoglycate eye drops to apply on your eyes as to ease the uncomfortable conditions. In addition, you had better buy a pair of sunglasses to prevent the sunlights from directly affecting your eyes when you are in the open on sunny day. Sunglasses with polarized lenses are better, and the dark brown and deep green colors are the best. Besides, you can also take in some cod-liver oil before sunbathing, and drink much water after it. If the condition of your eyes is very serious, you should not go to the beach again, and go to the doctor's for medical treatment as soon as possible in case of worse conditions.