I have used a chickweed salve and most bites clear up in a day or so.However I have one that continues to itch after several days, I had thought. It a chigger or mosquito bite.
Don't itch! :) Seriously, itching only makes it worse.
But my favorite herb for that is mashed fresh plantain (Plantago major) leaf applied to bite. Works great and is free. Look for it in any untreated lawn.
Regular laundry ammonia will neutralize the poison in most bug bites as well. It can be corrosive, so use with caution. I usually just apply a bit to the exact bite location with an earswab, and rinse off with water after the pain or itch begins to subside.
If your bite continues to be bothersome and develops an expanding pink area, suspect exposure to Lyme or some other disease and get it checked out.
Try aloe vera
How do you make the chickweed salve. I have tons of it growing in my back yard.
I make both plantain and calendula into salves. Dry the botanicals and add to olive oil when dry. Place in a warm place for 2-3 weeks and gently turn and rock it daily. Strain with cheescloth. Warm oil and add beeswax. A drop of mixture on a cold plate should give you an idea how firm the salve will be. Once you've added enough beeswax, pour in jars and cover. That's it. Simple and so useful! I use for dry skin, bug bites, and general skin complaints.
Definitely tea tree oil. You can buy it in "ointment" tubes or dilute the pure oil. You can also buy a tea tree oil spray that (for me) works very well for taking both the sting and itch out of mosquito bites in particular. I used the ointment for the aftermath of Queensland midges (sandflies) wanted to eat me for dinner. Stoped the wounds from becoming too infected. I also used medical grade manuka honey on the bites and there's almost no sign of the bites/scaring left. Both are readily available in Australia.