hi;
You are probably suffering from erectile dysfunction ;may be you are tired ;over worked ;or mentally under pressure .If so try to get over the mental hurdle & hopefully your erection will improve .For timing try start & stop method ;here you stop before orgasm wait for a minute then again start .repeat this few times & the time should improve.
thanks

Hello,
Welcome to HealthcareMagic. The size of an erect penis usually over 2 inches is normal. An erection problem is the inability to get or maintain an erection that is firm enough for a man to have intercourse. If the condition persists, the medical term is erectile dysfunction.

Causes may be psychological, smoking, alcohol, illicit drugs and medical conditions like diabetes, high blood pressure, heart or thyroid conditions, poor circulation, low testosterone, depression, spinal cord and neurological causes. To exactly pinpoint a diagnosis you need to get a complete examination done from a urologist. Hope it helps you. Regards.