Can u help me?how can i put on weight after lossing 5 kgs due to fever?

i had fever for d past 10 days and was kind of dehydrated because i vomited everything i ate..now i am feeling better...the problem is i have lost a lot of weight theses days..i was already thin before now i am even more..what can i do to put on weight..also tell me what is good for health and hygenic to eat!and does pickle make you thin..is it unhealthy..i keep eating it often..:)..thanks to all those who answer.!:)