so, i downloaded your craft ( the 2nd one)and started doing some trials....
is somewhat a mess.
-this is what KER read:
so i can already tell you that the craft is:
overengineered ( you need 3.4k+0.9k.0.4km/s of deltaV, you have them in the first 2 stages, not counting the 3rd), you could probably reach duna's orbit in stock
-also, as other have pointed out:
so your lab has no mean to communicate ( so you will lose control at some very early point) and can't generate power, so your lab can't run for more than probably an our before running out of electricity and can't even transmit back the data it developed.
-too much TWR ( thrust-to-weight ratio) at the launchpad, you are wasting a crapton of you power and are making your rocket very hard to fly.
-adding insult to injury to the last point ( hard to fly in the atmosphere)
1) you COM (center of mass, the yellow ball) is below the COL (center of lift, the blue ball) so your rocket will want to flip in the atmosphere ( you are trying to make an arrow fly backward)
2) aerodynamically speaking is a mess: you are not using adapter below your lab, so you have a crapton of drag , you don't have ( probably even researched yet) controllable flap/wings so flying it at high speed is very hard, and you don't have any probecore with at least SAS. ( in the 1st craft, the 2nd has it but is still underpowered compared to you aero's problems)
and those are the problem of the whole craft. talking about your payload ( your 2nd craft)
in vacuum, I started doing a burn without SAS engaged, and everything went normal ( you can see from the "thrust torque readout that it says "0")
.....then I engaged SAS....and this happened
as you can see the thrust torque readout from KER says 60kn-m, and the rocket started flipping like crazy
then i saw a little detail: THE PROBE CORE IS INVERTED!!!!!!! this is why your rocket starts flipping, when you give it a nudge the SAS will try to compensate, but as it is mounted upsidedown it will actually make things worse instead of correct it.
rotating the probe core resolved the issue
p.s. don't worry iwth your first carrees and rockets being a mess, that's normal and part of the (steep) learning curve of ksp, we all improve