There are over 4,000 new cases each year with perhaps ten times that number still unrecognised. Symptoms to look out for are discharge from the penis, itchiness, sores, blisters or pain in the genital area, pain when having sex or frequent urination. STDs can generally be treated but can cause long-term damage if not dealt with soon enough. Contact your GP if you have any concerns.
Sex is ideally part of a long term, loving relationship.
If this is the case, then be careful and consider using a condom. The BBC is not liable for the contents of any external internet sites listed, nor does it endorse any commercial product or service mentioned or advised on any of the sites. Always consult your own GP if you're in any way concerned about your health.