Thanks for your query,based on the facts that you have posted it appears that you have noticed colour of your semen has changed to yellowish since couple of days.
This is most likely to be due to presence of infection either in seminal vesicle
Please get your routine urine test and semen culture done to find out the organisms causing this infection and antibiotics to which they are sensitive to.
You need to take antibiotics like Doxycycline twice daily for 3-4 weeks to combat the infection completely.
Repeat semen examination after the completion of course of antibiotics.