Genital problems are fairly common. Unfortunately, because of the sensitive nature of the area and subject, people often defer medical treatment until the condition has progressed. I would strongly recommend that you see your primary care doctor
to have this evaluated. There are many possible causes for genital lesions -- some of which are serious and require medical attention.
To answer your question -- there is little to no difference between round or oval lesions. Any condition that can cause a round lesion, can also cause an oval lesion. There is certainly no way to rule out a specific condition because of that shape. Often the shape is determined by where it is located (say for example on a skin fold). The shape can be helpful in determining smooth bordered round/oval lesions versus a more irregular bordered lesion -- but even this is not definitive.
It is advisable that you see your doctor. Without more information it is difficult to help with the diagnosis. Syphilis, herpes, chlamydia, HIV can all cause skin lesions. In addition, primary skin problems like skin cancers or inflammation can be responsible. This is important as you may be putting yourself and your sexual partners at risk.
Talk to your doctor to have this evaluated. Good luck!