Your clutch needs adjusted or replaced.
If it will go into gear when the engine is off but not when the engine is running, the clutch is not disengaging. It could be the clutch, possibly warped or put in wrong, or it could be the hydraulic clutch mechanism.
Vacuum lines, clutch switches, ...
Could be a broken clutch fork, linkage, or cable depending on the setup.
If it does this in all gears, I bet your clutch is shot. Other things that could cause problems are the Clutch master cylinder or clutch slave cylinder.
There could be a number of reasons why your truck will not shift properly. There could be something wrong with your clutch or transmission.
Could be a blown fuse, low of refrigerant, defective A/C clutch, broken or slipping A/C belt, or as simple as the wires to the A/C clutch disconnected.
A warped or otherwise damaged clutch disk or a faulty clutch master or slave cylinder could be preventing the clutch from completely disengaging when you depress the clutch pedal.
it might be the slave cylinder
If your rabbit has discharge coming out of its eyes, or has sticky or crusty eyes, there could be any number of things wrong (a parasite, disease, abscess, injury; the problem could also be dental; so on and so forth), but whatever the cause, the rabbit requires veterinary attention immediately.
im thinking you need a new clutch.
Yes, of course it could be wrong. However, "feeling sick" could be due to the flu, a hangover or any other illness. Most pregnancy tests are pretty accurate. Good luck!