I recently just got a free Xbox live gold trial and have been playing on it for a few days now and I’ve leveled up my character quite a bit and got many things for it in req packs and today I tried to go on and now all my data is gone is says I’m back to level one and I can’t go online even tho the membership is still active

Sounds like a profile sync error. Your data is stored on 343i’s servers; you can check your Waypoint profile to verify your level is where it should be (level 12). Many users report that a hard reset of the Xbox fixes profile sync errors; worst case scenario, you may need to reinstall Halo 5, or delete your local save data from only your Xbox (not everywhere). But try a hard reset/power cycle first, and see if that clears things up.