Answer
(Fatwa: 1253/L=310tl=1431)
First, you should remove this problem and contact any expert hakim. Avoid bringing sexual thoughts in mind and reading immoral SMSs. As far as the matter of offering salah in the abovementioned situation is concerned, if drops of sperm are really discharged i.e. it is thick and organ gets loose after discharge, then only doing istinja will not be enough to get taharah rather ghusl will be compulsory. The salah will not be right if you offer it only by doing istinja.
Allah (Subhana Wa Ta’ala) knows Best
Darul Ifta,
Darul Uloom Deoband