Allergies nt getin now

Patient: Sir i get cough cold after night fall before that two three days i get some digesive prob food undigestion .and is there any thing that after n8 fall iget ill cough cold fever attach at once suggest me how to develop immunity power i am 23yrs old and getin these prob 6yrs later that,s why body became weak i suffer ill in aprox every month or in 15days.