Questions Before I Start

Recently I took about 12mg of tianeptine and experienced a lot of euphoria. I know this a selective serotonin reuptake enhancer but what about gives this euphoria?

Other SSRIs/MAOIs take weeks to take into effect. What is it giving euphoria so fast?

Also, I know the standard use for depression is 12.5mg 3 times a day but won't that build tolerance? My last question is, how frequent can I keep taking tianeptine without noticing a tolerance increase? Also, what receptors does this tolerance build up on?

TLDR: What causes the tianeptine euphoria? How often to take without building up tolerance?