Hi there and thank you for your question.
I appreciate your concern here and I shall try and help where I can.
Bramble thorns break off quite easily and can lodge under the skin due to their size and sharpness. The issue though is that the tips of the thorns tend to break off and embed themselves under the skin.
In effect, the body regards this splinter as a foreign body under the skin and an inflammatory reaction occurs. Blood rushes to the site of the wound in order to get white cells in the area so as to try and destroy the foreign body. That is why the finger would swell and become red and tender.
The swelling then came down as you removed the splinter and the healing process can continue without there being a foreign body in the way to complicate matters. The clear fluid would be plasma that escapes which was formed as part of the initial foreign body reaction.
You can continue applying the antiseptic cream for a couple more days just to help prevent an infection from occurring. The issue should then resolve on its own with the swelling decreasing on a daily basis.
If the swelling, tenderness and
redness starts to worsen then I would suggest seeing your doctor to assess the situation. Either there's then a secondary infection or there still is a foreign body stuck at the site of the wound.
I hope this helps and good luck.