Oh no!! Baby is sick!!
Once the baby arrives every little sniffle,cry, cough feels like the end of the world!

Accept the fact that despite your best attempts at protection baby is going to get sick.

The first sign for me is a fussy baby, who deviates from normal behaviour or routine.

A child who cries endlessly and is  inconsolable is never normal.
Few tips that maybe helpful-

1) Find a pediatrician. Trust him or her.

Do your research and ask around for someone who will match your ideology of parenting and be available to answer your queries.
No Dr. Google

Google is a great resource if used safely.

But it is not a replacement for medical advice from a doctor.

Even worse- using Google to give advice to other mums!(yes I've seen it happen).
2)DO NOT self medicate.

Most pediatric dosages are based on weight, so you dont want to over or under medicate your baby by deciding for yourself.

Ask your doctor for dose and frequency, not the chemist or family member or your friend.
3) Do not ignore a fever

They tend to escalate rapidly at times with bad consequences. Always measure and monitor. Whole body sponging works very well to bring the temperature down. I've spent entire nights doing this.
4) Home remedies

We all try to avoid medicines. But if you have been advised medicines then  try use home remedies alongside what your doctor prescribes, not as a replacement.

Eg. A child with ear pain may need meds. But if you are just putting oil etc in the ear you maybe doing more damage than good.

Also, when your neighbour tells you to use xyz as it worked for her kid, it's not necessary it will work for yours.
5) Make a note of questions and discuss with your pediatrician!

It will make you feel much better and in control of your child's health.
6) Let it go!

Kids won't eat well when sick, dont fret about it.

Do not give too much importance to chubby or leanness.

My chubby child has had more sick episodes than my somewhat-lean child!
But remember things will gradually fall into place and your maternal instinct will guide you to what's really a problem and what isn't.