Thank you for asking.
Your symptoms are consistent with a condition called "premature ejaculation". A condition in which the time duration for ejaculation while an intercourse is short. Because of which, the couple is not able to enjoy a normal sex.
Faulty masturbation technique/habit, innate anxious tendency are some associated factors that I noted in your case.
Viagra will not help you obtain any benefit. It is rather indicated for an erectile dysfunction and not early ejaculation (your case). Therefore, do not use viagra or similar group drug.
Condoms imparts a bit of insensitivity to penile skin while its use during sex, and therefore it is because the penis has become less sensitive, that you reach climax late and hence ejaculation gets delayed.
Next Steps
My suggestions : 1) Consult Psychiatrist/Sexologist, as he can prescribe you medicine that will prolong the ejaculation time. 2) Education about sex and healthy masturbation is must. Therefore, you both as couple need a Psychoeducation session. 3) A technique called "Directed masturbation", can help you learn proper way of masturbation and with the ejaculation problem.
Health Tips
With proper medication and Psychoeducation you can enjoy fruitful sex. Do visit a sexologist. Regards, Dr Pankaj B Borade