The feeling of being watched in Hillsborough County, Florida

I was leaving saint petersburg with the intentions of hitch-hiking to asheville, nc. I had a friend drop me off at the I-75N XX exit around 11 pm. there was a lot of construction going on and since it was getting late I decided to camp for the night. I walked to the bridge that crosses the XX river. I was planning on sleeping under the bridge, I walked down underneath, got myself comfortable then I heard a couple of noises to the left of me (coming from the southbound bridge)I played it off as a possum or raccoon, then I heard it again.. so I decided to move closer to the river and hang my hammock in between two trees. I was texting people, then called my friend and talked to her until about 2:30 then we got off since my phone was about to die. I went to sleep pretty quickly afterwards... but not for long. I woke up to a noise down by the river to my left. it was a weird cough/grunt that I can't really explain. I can't mimic the sound but I only heard it once. 10-15 minutes later I hear another sound, this time a low whistle from my right, next to the tree line. it lasts 5 or 6 seconds. I continue to lay there in silence. another 10-15 minutes go by and I start hearing rocks being thrown at me, this happened 5 or 6 times, every couple of minutes or so. then more silence... not sure how long it lasted but it was followed by the loudest crash I have ever heard. I thought the tree I had tied my hammock to cracked. I almost fell out. it sounded like thunder/gunshot/dynamite going off in my face. after that I made up my mind to leave, quickly packed up my hammock and headed back up the hill. crossing the bridge, I caught a quick whiff of a skunk like smell and can feel a set of eyes on me. after that I decided to catch the bus back to NC.