Navgrah are the 9 planets and they are connected with their deity lord viz, Mars the ruling devta is Mangal dev and the deity is Hanuman ji. If planets are giving adverse or unfavorable results in the life of the individual this is due to the unfavorable planets having the main period of Mahadasha or there should be any malefic planets will transiting over the adverse so on.. all depends upon the condition of the planets.
We can perform Nvgrah pujan in any occasion, this is not mandatory to perform Navgrah pujan only when you are in trouble, this will be the another reason. But in general we can preform pujan to get auspiciousness of the navagrah.
Short answer of your query. Of you are getting the trouble after doing navagrah pujan it means that you need to put your devotion for the navagraha first.. then it might be possible that any malefic planet such as Shani Rahu or the Ketu is transiting over the malefic houses in your horoscope. Due to the slow moving property of these malefic they takes long time to pass through one sign and native faces problems for the long this. So don’t worry just do remedies to mitigate the evil effects of the planets.
I hope this answer will be helpful for you.
Thanks
Astrosubhash 