I expect a lot of people are losing out of the blinds if you include the blinds you have to put in. Ignoring the mandatory blinds, it'll still be your least profitable position but you shouldn't be a huge loser there

Certainly when I'm SB v BB I try to play small ball poker. I'll have to check what my results are for the blinds more generally but those do seem very high. Maybe you're defending too wide/limping in to too many pots with trash because of 'great pot odds' and not being able to take the hand anywhere?

Its absolutely normal that you lose in SB and BB.

And its normal that you are losing more from BB than SB.
Proper winrate i belive is around -15bb SB -30BB BB

I've been looking at some threads on other forums about this and it seems that no-one is positive, and anywhere between -10 to -40 can still be profitable overall. It would seem that -20 in the SB and -40 in the BB is about normal although -15 and -30 would be desirable.

I think if you fold the BB and SB every time your win rates would be -100 and -50 respectively. Therefore, you are effectively still 'winning' in the blinds by losing less

Some pointers for the SB:

-3B more loose CO/BTN opens (applies for bb as well)

-Mix 3B/flatting low and middle PP`s (applies for bb as well)

-Steal a ton from tight BB`s with marginal hands. 

For the BB:

-Widen your value 3B`ing range vs loose Sb steals.

-3B tighter Sb opens with more polarized ranges/blockers.

-Sqz more with strong aces (AT+) and with blockers.

These are just off the top, i`m sure some of the guys will come up with more suggestions.

Very important note:

If you already have a steady/winning strategy you should be very careful about what you implement in your game.My suggestion is that if you don`t feel comfortable making some or any of these adjustments you should just play the game that works for you.