Luciana, I use crystals to protect me. Until you learn to shield yourself, it's easier. Somedays you don't have the energy or time to shield yourself....use crystals. Now I use quartz, red lace agate, snowflake obsidian, and many others. It depends on what I am drawn to that day.
It's the same when you buy them. Go towards what you are drawn to.
It's also good to try to ground yourself daily. the easiest way is to walk barefoot outside. That's a bit hard where I live in the winter. That's when I visualize going down into the earth, to ground myself. Inbox me if you like and I'll find some links for you to read.
As for meditation which helps a lot, when you are busy it's a challenge. Sometimes you only get a few minutes to yourself in the loo. Sometimes, while I clean my home, I light my candles, and some incense, put on some soothing music and meditate while I clean my home,. It's not the best of circumstances, but some days it's the only way.
First: make sure your brain agrees to concluding 'it is not your problem'.
Second: Try visialising a seethrough membrane very close around you and then expand it to secure your personal space.
Third: breathe in and out calmly.
Fourth: Think of something nice you can do in a few minutes
Fifth: Leave the bad aura calmly.