If I had oral sex a month ago and I swallowed the cum and I think I contracted a std wouldn't my mouth be a mess or there are no symptoms?

STD after oral sex. Oral sex does carry the risk of contracting an STD and it unfortunately there isn't much data on the risk of STD from simply swallowing sperm. Oral sex puts you at risk if your partner had any sores on his penis and they can be asymptomatic HIV risk from oral is extremely low. Knowing your partner is the best suggestion. See ttp://www.sfcityclinic.org/stdbasics/stdchart.
Usually no symptoms. Despite what you might have been told in sex ed or seen online, oral sex can be considered safe sex. There is some STD risk, but a lot lower chance than vaginal or anal sex. Swallowing semen or not makes no difference. Most oral STDs cause no symptoms at all. Every sexually active young person should be tested for common STDs from time to time. See your doctor, tell all, and follow her advice.