How do I improve my sex time? When I do sex my sperm comes out in 30 seconds I am 18 years old boy and I am so weak in sex can anybody solve my problem without any side effect?

FOCUS. On partner and partner's pleasuring. Stop what you are doing / pull out if necessary, and attend to stimulating partner for 20-30 seconds (not so long as to go soft), then resume. Use stroke force and pace to help build to (not rocket past) climax, and then slow down/remove, stimulate another part of partner. Works for many. Can google "squeeze technique" or try numbing med inside condom as other.
This . This is called premature ejaculation. Therapies include medications such as those that delay the arousal response (oral medications such as selective serotonin reuptake inhibitors, creams or gels that diminish the sensation), partner therapies (start and stop technique), and the method of gaining control instead of prevention (excercises to gain control of the muscles involved in ejaculation).