[Riftmaker]

If you had items that gave you + Con or + HP, they would be removed during the importation.

You will only be level 7 at the start of BG2, unless you did TotSC, in which case you would be level 8.

Given you are level 7:

7*10 = 70 (that's IF you had maximum hit dice rolls enabled during BG1, if you didn't it would just take the HP from your character file). After that it adds the Con bonus.

Theoretically that would be 35 if your constitution really still is 19.

Check to see what your CON is in BG2, and adjust accordingly. If you finished BG1 with 90 hp, then you only had 55 of 70 possible HP from actual hit dice.

You take that, and add 7*3 (21) and you get 76.

My theory is that BG2 read your actual HP from hit dice (55 given by 90 (what you said you finished with) - 35 (CON bonus when CON is 19)), and added the new CON bonus (in this case your CON somehow went down to 17). Check to see what your new CON is, then reply back. If it's still 19, then the problem may correct itself when you gain another level.