Regarding answer to your first question about speech of your child who is nearing 2 years of age is that if he understands and responds to when called or talked to, carries out simple commands, and says amma, appa etc to these relations with meaning, and has a vocabulary of about 30-40 words, I think there is no need to worry. Some children have slightly delayed speech, specially if one of the parents had similar speech. You can talk to your child, recite nursery poems, read stories to him and stimulate him with words, it will enhance his speech. If in the next 3 months there is no increase in spoken speech, you can consult a doctor to test his hearing and also to see that other developmental fields are normal.
Your second question about frequent colds, it can be allergic or infections. I presume your child is vaccinated well. You should consult an ENT specialist to check the ears for otitis media or sinusitis and advise proper treatment. If there is fluid in middle ear that can also effect speech as hearing gets impaired. Homeopathic medicines take a longer time to treat, may be if you continue for longer period you will find better results.